ings. Great care should thus be exercised in order that only suitable moss be collected. To this end it is often wise to carry a sample of approved sphagnum for comparison until one is quite familiar with the work. In the bog it has been found most convenient to take a small handful of moss at a time and to shake it lightly to get rid of most of the foreign matter, such as leaves, twigs, roots, etc. If wet, squeeze out as much water as possible before putting it in the bag, but do not wring it, as that will break and injure the stem. The depth to which usable moss extends varies with the species and environment. In many cases beds of Sphagnum imbricatum may be worked to advantage a foot to eighteen inches or even farther, depending on whether the plants remain intact or whether a partial decay has begun. In general, whenever the plants begin to break up as a result of the first stages of decay, they must be discarded; but as long as they remain intact, with stem fairly well crowded with lateral branches, they may be used, the color playing little or no part in determining the suitability. While gathering moss it is wise to secure all the good moss in a given space before proceeding to another, because after a growth has once been disturbed the adjoining plants usually deteriorate and sometimes die. After it is taken from the bog the moss should be removed to some shelter and spread out to dry. This may be done on the grass if the weather is fine, otherwise on suitable racks which usually prove more satisfactory, or on the floor of some empty building, although care must be taken not to put it on valuable flooring, as the dampness is apt to do some dam age. The collection of moss is one of the most important phases in the making of sphagnum pads. Much depends upon the condition of the moss when it reaches the sorter if their work is to be most efficient. It has been found that carelessness or thoughtlessness on the part of the collector often decreases the efficiency of the sorter far out of proper proportion. The most tedious part of making sphagnum pads is picking over and sorting the moss, and this is greatly increased by careless gathering. The sorting should be done in some central place and completed before the moss is dry. If inadvertently the moss becomes too dry it should be spread out in a gentle rain for a short time or sprinkled with water and left over night with an oil-cloth spread over it. HOW SPHAGNUM PADS ARE MADE Like many other things in connection with this war, the directions for making surgical dressings from sphagnum have not been static, but progressive. From time to time valuable suggestions as to where the pads could be improved have been received from surgeons at the front who have been actually using them. Acting on these suggestions, the British have gradually increased the efficiency of their moss dressings. More recently the American Red Cross, after some experimentation under the direction of Dr. John A. Hartwell, has adopted a different dressing which promises to be even more efficient than the one authorized by the British War Office. But the last word has not yet been said on sphagnum for surgical dressings. The American type of sphagnum dressing is composed of gauze, a thin sheet of wood pulp paper, non-absorbent cotton and sphagnum. The sizes of the dressings will vary from time to time as the War Department may recommend. The first half million pads allotted to the Northwest Division of the Red Cross consists of two sizes, 8 in. by 12 in. and 12 in. by 24 in. In making one of these dressings, a piece of Zorbik or Scott tissue of appropriate size is placed on the table and on it a wooden frame corresponding to the particular size to be made. The frame, which is about three quarters of an inch deep, is filled evenly with moss over which a thin layer of non-absorbent cotton is placed and then the frame removed. The margins of the tissue are then folded over the cotton and sphagnum. It is usually convenient to use spring clothes-pins to hold 4 Zorbik or Scott tissue is a very thin wood-pulp paper used to envelop the sphagnum and prevents it from sifting out. the ends in place, although this is not absolutely necessary. In order to keep the outside covering free from particles of moss it is best to remove this incomplete pad to another table where there is no moss. Here it may be finished by the same worker or by another. A piece of gauze of appropriate size is spread out on the table and the incomplete pad is placed in the center of it, with the non-absorbent cotton up. A thicker layer of cotton is then put over the pad, extending about a quarter of an inch beyond the edges. The gauze is folded over the pad so that the long fold is on the back, that is, on the side next the non-absorbent cotton. The open ends are folded in "muff-wise," first folding the under side up over the tissueenvelope, then folding the upper side to correspond and adjusting the "muff-end" carefully. The pad is patted lightly to make sure the sphagnum is evenly distributed throughout and then passed through a clothes-wringer. If, when held up to a strong light, "holes" are detected in the pad, too little moss has been used. If the pad is solid and harsh, there is probably too much moss. The British type of sphagnum pad consists of a flat bag made of English long cloth with a fine enough weave so that the particles of moss will not sift through. This bag, which varies in size according to the need, is filled with the appropriate amount of moss and sewn up. The Canadian Red Cross adopted three types of sphagnum dressings, the British type just mentioned, a standard dressing similar to the American type and bed pads made of second grade sphagnum. During the summer (1918) the Canadians are concentrating most of their energy on the standard dressing, while a smaller number of the British type and comparatively few of the bed pads are being made. SUMMARY 1. The use of sphagnum as a substitute for absorbent cotton is not only a great saving of money but is fast becoming an absolute necessity on account of the acute shortage of cotton, due, in part, to the extensive use in explosives. 2. It has been estimated that if absorbent cotton were used exclusively in the hospitals the cost would be not less than $200,000 per annum for Great Britain alone, while the cost of the moss is practically negligible. 3. The value of sphagnum as a surgical dressing lies chiefly in its absorbency. The species used for this work will absorb and hold fourteen to twenty times their weight of water. Ordinary absorbent cotton will hold only four or five times its weight. 4. The sphagnum is not subjected to any special treatment for surgical dressings but simply gathered from the bog, the foreign material removed, dried and made into pads which are sterilized after they get to France. 5. There is some indisposition on the part of American surgeons in France to use these pads. This is what was anticipated as surgeons are, to say the least, conservative in connection with their supplies, etc., and generally speaking indifferent as to the expense of these supplies. The British Army Medical Service went through the same thing two years ago and even up to last year sphagnum dressings were looked upon as an undesirable make-shift by a great many British surgeons; but at last they seem to have come into their own, as can perhaps best be illustrated by the fact that Canada has been given an allotment of 20,000,000 and that Scotland has been recently asked to turn out 4,000,000 sphagnum dressings a month. 6. Although sphagnum for surgical dressings has been largely the result of the present war, a make-shift for a necessity that had arisen, yet there seems every reason for believing that it is not going to be discarded after the war ends. The inexpensiveness of the moss, its high absorbency, its abundance in certain parts of the country and its undoubted superiority over gauze and absorbent cotton for some purposes, clearly indicated that it is too important as a hospital equipment to let die with the war. When the war is over it will probably take its place among the regular commercial products called for by modern hospitals. 7. The last word has not yet been said regarding sphagnum for surgical work. Ex periments are constantly going on, looking towards both the improvement in these dressings and also in the extension of the usefulness of sphagnum along other lines. J. W. HOTSON THE UNIVERSITY OF WASHINGTON, SEATTLE, WASH. A NEW SEASONAL PRECIPITATION FACTOR OF INTEREST TO GEOG RAPHERS AND AGRICULTURISTS Most persons who have attempted to correlate soils and vegetation with atmospheric precipitation have directed their attention chiefly to the total annual rainfall and its variations from place to place. It has long been recognized that seasonal distribution also needs to be taken into consideration, but there has been no unanimity as to how seasonal variations of rainfall should be treated. Some have simply mapped the total precipitation for each month or season separately, or indicated the months of maximum rainfall in different regions; but a more common method has been to map the percentage of the total occurring in the six middle months of the calendar year, April to September inclusive. Such an arbitrary division is rather unscientific, however, for in the eastern United States, if not throughout the northern hemisphere, the warmer half of the year usually extends from the latter part of April to the latter part of October, so that May to October inclusive would more nearly represent it. The use of the earlier period has been defended on the ground that April rain is more beneficial to crops than October rain, which is probably true (and so would March rain be better than September rain); 1 For such correlations between soil and rainfall see Bulletin 3 of the U. S. Weather Bureau, by E. W. Hilgard, 1892. A review of this, which may be more accessible than the original, can be found in the Experiment Station Record, 4, 276-282, October, 1892. 2 For a map of the United States on this principle see Plate 2 in U. S. Geological Survey Water Supply Paper 234, 1909. 3 See Geol. Surv. Ala. Monog. 8, 24; Bull. Torrey Bot. Club, 40, 395, 1913. but the type of rainfall that is best for crops, other things being equal, is not necessarily best for soil in the long run. A warm rain presumably has a greater leaching effect than cold rain or snow, and regions subject to heavy summer rains, like most of Florida, generally have poorer soils and more swamps than where the summers are dry, as in California.* In recent years the writer has calculated the rainfall percentages for May to October and also for June to September for numerous stations in the southeastern states, and thereby shown some interesting correlations with soil and vegetation. But when these factors are mapped for the whole United States the correlation does not work out so well. For the northern part of the Great Plains has about the same proportion of its total rain in summer as peninsular Florida, but very different soils and vegetation. Of course part of the difference is due to the fact that the total rainfall and average temperature are much less on the Plains than in Florida. But there is another important climatic difference. In the Great Plains and much neighboring territory the bulk of the rain falls in early summer, while along the Atlantic and Gulf coasts there is generally more rain in late summer than in any other equal period. Consideration of this fact recently led to some comparisons between early and late summer rainfall for the whole United States. After some experimenting it was found that the most striking results were obtained by taking the difference between the rainfall for April to June inclusive and that for August to October inclusive, the former being good for the 4 Dr. A. D. Hall, of Rothamsted, in an address on agricultural extension problems published in the Popular Science Monthly for October, 1914 (p. 349), says: "Winter rain is more valuable than 5 See Bull. Torrey Bot. Club, 37, 415-416; 40, 395; 41, 556-557; Geol. Surv. Ala. Monog. 8, 19 24, 36, 1913; Fla. Geol. Surv. Ann. Rep., 6, 182184, 1914; also Ward in Bull. Am. Geog. Soc., 46, 47, January, 1914. 6 If climatological data for fractions of months were available we could include the first half of July in the early summer period and the second crops and the latter bad for the soil. Data for a few hundred stations were taken from Bulletin Q of the U. S. Weather Bureau, which although it brings the records down only to the end of 1903, and contains a few typographical errors in the figures, is easier to handle than any later publication covering the same ground, and is probably accurate enough to base a working hypothesis on. The resulting map differs considerably from any other precipitation map, but instead of publishing it in its present imperfect state a brief description will be given. The line of equilibrium, where there is no difference between early and late summer rainfall, crosses the St. Lawrence River in northern New York and extends in a general southwesterly direction, with various sinuosities (perhaps due largely to differences in altitude and exposure between neighboring weather stations in the Appalachian region) to the vicinity of New Orleans, thence westward, passing between Houston and Galveston, to near Del Rio on the Rio Grande, northwestward across the Staked Plains to the Rocky Mountains in Colorado, westward to Monterey County, California, and then southeastward just back of the Coast Ranges into Mexico. Another part of it separates the northern half of Michigan, northeastern Minnesota, and part of Wisconsin from the states to the southward, then passes northwestward into Canada and dips back into the United States just enough to cut off the north end of Idaho and the northwest corner of Washington. The borders of the United States are mostly in the region of late summer excess, while approximately three fourths of the country, including almost the whole area drained by the Mississippi River, has an early summer excess. The greatest late summer excess, about 11 inches, is on the east coast of Florida, and the mouths of the Mississippi and Rio Grande are not far behind. The Black Hills have an early summer excess of half in late summer, and perhaps get still greater contrasts. Nassau in the Bahamas, about 180 miles farther east, has a late summer excess of nearly 13 inches. about 6 inches, and the area having more than 4 inches extends all the way from Montana to Alabama. If ratios instead of differences had been used the position of the zero line would have remained the same, but the gradient would have been steepened in the drier parts of the country. The map here described suggests at once some very interesting correlations. Considering other climatic factors first, nearly all our tornadoes occur in the region of considerable early summer excess of precipitation, and our hurricanes in that of considerable late summer excess, while regions where the difference is. not more than an inch or two either way rarely suffer much damage from wind. Both tornadoes and hurricanes usually occur during the period of greatest rainfall in their respective regions.8 The late summer rains commonly come in the form of showers in the daytime, while the 8 There is a tornado frequency map of the United States by J. P. Finley in Professional Paper No. 7 of the U. S. Signal Service (1882), reproduced on a smaller scale with fewer details by R. DeC. Ward in Quart. Jour. Roy. Meteorol. Soc., 43, 323, 1917. This is based on 600 tornadoes occurring between 1794 and 1881, but is a little misleading, because in the early part of that period the regions where tornadoes are most frequent were practically uninhabited by civilized man, and thus the apparent frequency of such phenomena in the older states is exaggerated. Of the 40 tornadoes prior to 1850 reported by Finley, 9 were in New York, 5 in Ohio, 3 in Connecticut, 3 in Georgia, and none in Kansas and Illinois, which now lead the list. A map based on records from about 1870 to date would be more accurate; but even Finley's map shows a fair degree of correspondence between tornadoes and early summer rainfall ex cess. It appears from Bulletin X. [not 10] of the U. S. Weather Bureau, on Hurricanes in the West Indies, by Dr. O. L. Fassig (1913), that there are only three well-marked hurricane regions in the northern hemisphere, all lying between latitudes 5° and 30° N., and all having a maximum storm frequency in September. In the United States hurricanes are most frequent in Florida, but they are occasionally felt as far north as the coast of Massachusetts. early summer rain is more likely to fall gently, and at night. In the southwestern semi-arid late summer rain area (i. e., Arizona, New Mexico and adjacent territory) the railroads have been put to considerable expense to build dikes to protect their tracks from sheet-floods following summer showers, while in northern Nevada and Utah, where the total precipitation is about the same, but its seasonal distribution different, no such precautions seem to be necessary. Floods of the ordinary type, caused by overflowing rivers, are much more frequent and destructive in the region of early summer rains, however. If there was such a thing as a soil fertility map of the United States it would be seen at once that the most fertile soils are in the region where there is more rain in early summer than in late summer, and vice versa. Considering texture only (for we now have much more complete data on that than on chemical composition), we can ascertain from published soil surveys that silt loam-which is usually considerably above the average in fertility is one of the commonest types of soil throughout the Mississippi valley, whether it is derived from weathered Paleozoic rocks, as in Tennessee, from glacial drift, from glacial lake deposits, as in North Dakota, or is of æolian origin, as the loess of Arkansas and Mississippi is supposed to be. Clay loam and stony loam are other common types in the same area, nearly or quite as fertile as the silt loam, while sand is chiefly confined to the banks of streams. The black prairies of Alabama and Texas, characterized by very fertile calcareous clays, are both in the area of early summer excess of rain, although when semi-annual percentages only were considered, as heretofore, the line of equal summer and winter rains passed between them. One would naturally suppose the flood-plain of the Mississippi below the mouth of the Ohio to be one of the most fertile tracts in the world; and so it is where it has more rain in early summer than in late summer, and most of the farmers in that portion use no commercial fertilizer whatever. But in several parishes below New Orleans, where the late summer rain is in ex cess, the average expenditure for fertilizers in 1909 was over a dollar per acre of improved land! (For the whole United States at the same period the average was about 24 cents.)9 The regions of heavy late summer rain are characterized by poor sandy soils, classed by the U. S. Bureau of Soils as sand, sand-hill, sandy loam, fine sandy loam, etc., and silt loam and clay are comparatively scarce. The sandiest extreme is in peninsular Florida, but northern Michigan, Cape Cod, and southern Texas are also notoriously sandy. Swamps too are about as prevalent in northeastern Minnesota and northern Michigan as they are in Florida. Although the late summer rain area covers only about one fourth of the United States and produces considerably less than one fourth of the crops, it uses at least three fourths of the commercial fertilizer; the average annual expenditure for that in some of the southeastern counties of Florida at the time of the Thirteenth Census being about $30 per acre.10 And even in California there is considerable fertilizer used in the southeastern portion. In all these eastern sandy and swampy areas the streams carry very little sediment and do not fluctuate much. In the corresponding parts of the Southwest there is not so much sand, but the type of soil known as adobe (and used extensively for building material) is very characteristic. The distribution of vegetation types is of course correlated with the soil to a considerable extent. Except in the Northwest the forests of the early summer rain area are composed almost wholly of deciduous trees, and there are vast areas of prairie; while conifers, especially pines, predominate in northern Wisconsin, Cape Cod, southern New Jersey, Florida, and many other places where there is more rain in late summer. The most extensive pine forests in North America are said by Professor Sargent11 to be those of western 9 In this connection see SCIENCE, II., 42, 500503, October 8, 1915. 10 See Geog. Review, 4, 225, September, 1917. 11"Manual of the Trees of North America" (1905), p. 16. |