A

T all events, it is the germ of So much is abplant cancer. solutely certain, and the discovery is of great scientific But the and practical value. chief importance of the "find" lies in the hope that it will point the way to a solution of the dreadful problem of cancer in human beings.

Plant cancer is the disease commonly known as "root tumor," "black knot," or "crown gall"-the last of these names referring to the fact that the morbid growths concerned often appear at the But they top, or crown, of the root. frequently occur on the stems, above ground, or even on the leaves.

The malady attacks many kinds of plants. It does a great deal of damage to fruits and vegetables, and has long

been known to be highly infectious-so much so, indeed, as to be readily communicable to a healthy plant by the simple process of binding a serap of tumor Hence it tissue upon a fresh wound. was to be inferred that a specific germ must be accountable for the mischief. But, if so, what kind of germ? That was the puzzle. For a long time all efforts to discover the organism were unsuccessful, and the experts almost made up their minds that none such existed.

This was the state of affairs when, in February, 1904, a New Jersey florist, engaged in growing daisies on a large scale, sent to the Department of Agriculture, for examination, a number of plants of hothouse daisies, both yellow and white varieties. All of them bore

Accordingly, in the hope of finding such an organism, fresh daisy tumors were crushed in beef broth, and small quantities of the latter were used for making gelatin "cultures." The gelatin (poured into glass saucers) afforded a suitable food for bacteria to grow upon, and, as a result, colonies of four different species developed. Three of these were yellow in color, and one was white. The next thing to find out was whether one of these was the tumor-making microbe.

To decide this all-important point, healthy daisy plants were separately inoculated with each one of the four kinds of bacteria. In each case part of the stem was first sterilized (i. e., made germ-free) by washing it with a mild solution of corrosive sublimate. Then the tumor-germ stuff was smeared upon it with a sterile platinum needle, and was thereupon pricked into the tissues with a sterile sewing needle. As a result, nothing happened to any of the plants

THE HOTHOUSE DAISY. WHICH GAVE THE FIRST CLUE TO THE PLANT CANCER MYSTERY.

tumor-like growths on one part or another of the stems and leaves. The smaller tumors were green in color, rather smooth, and soft and spongy in texture. As they became older and bigger, they darkened to brown, and grew hard, rough, and corky.

Some of the plants, at the Department, were set out in the "pathologic hothouse"-a sort of vegetable hospital, in which the potted patients are inoculated with various diseases and watched for symptoms-and, while under observation, many new tumors appeared on them. It was decided that the morbid growths could not be due to injury by insects; and there was no sign of any fungus enemy. It seemed reasonable, then, to infer that some kind of bacterial germ was responsible for the

TWO INFECTIONS OF CLOSE IDENTITY.

1. occurs in hothouses, supposed, at first, to be crown

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inoculated from the yellow colonies, but those treated with the white culture promptly showed signs of

infection. In less than three weeks knotty growths appeared at every point where a white-culture puncture had been made.

Thus it was that the discovery of the germ of the disease which causes tumors in plants was finally made. It was afterwards confirmed by a long series of experiments, the results of which will be summed up later on. Incidentally it was proved that the organism in question called by the finders, Dr. Erwin F. Smith and Dr. C. O. Townsend, Bacterium tumefaciens-is the same for all plants which the malady attacks. But, in the meantime, it is appropriate to ask why the tumors are called cancers, and what relation they have to the malignant growths so designated in human beings and the lower animals.

Well, in the first place, the plant tumor is in structure so like a cancer

CULTURES OF THE CANCER GERM.

A. on daisy four days old: b. on daisy eight days old c. peach-gall; d, hard-gall of apple at end of five days, after being used for inoculation; e, same as a; f, daisy organism after a number of days; g. old tube of sterile milk: h. similar tube inoculated for two months with the daisy cancer.

that there is really not very much difference between the two. In both cases there is the same enormous proliferation of cellular tissue, often forming nestlike masses. Under normal conditions, in plant or animal, cells of each class have their own particular work to dothe making of secretions, or what notbut in a cancer, or a plant tumor, they are no longer attending to their business, and seem actually to have gone crazy. Even when viewed under the microscope, the structure of a plant tumor is found to differ in no important respect from cancer in a human being.

Just as the tumor disease attacks plants of many species, so does cancer

human beings, when they have been cut out. Another, and even more striking, phenomenon is the appearance of later and secondary tumors in plants, some distance away from the first seat of infection-such secondary growths being produced seemingly by the migration of cells from the part originally diseased to other portions of the structure. They are probably carried by the water current flowing through the tissues of the plant. In the same way, cancer cells in man travel through the blood vessels and lymph channels, and start fresh growths in the vital organs-this being the last, and soon fatal, stage of the malady.

In either case the trouble is a malignant overgrowth, due to a vastly rapid multiplication of cells. This growth, in the plant, proliferates indefinitely, and, assuming a parasitic character-just as in man becomes a wasting disease. It does not seem to be able to obtain enough water and nourishment to carry it beyond a certain stage of development, and portions of the morbid tissue soon slough off, necrosis-death of the part affected-following.

The knowledge, gained as long ago as 1900, that healthy plants could be inoculated with the tumor disease by grafting

Two EXAMPLES OF TRANSFERRED CULTURE. 1. daisy on sugar beet: time, 10 months. 2. peach on sugar beet: time, 54 days.

INFECTION FROM PEACH ON GERANIUM. Time of development, three months.

tumor tissue upon them, placed the vegetable pathologists ten years ago in exactly the same position, in relation to plant cancer, as the animal pathologists find themselves in today with regard to cancer of human beings and other animals. The animal pathologists are able, at the present time, to produce cancer artificially in mice and other animals by introducing pieces of cancer tissue beneath the skin of healthy individuals. But this is as far as they go; they don't know the reason why.

Less than ten years ago the vegetable pathologists imagined that there was no germ of plant cancer, because they could not find it. Today most of the animal pathologists assert that there is no microbe of animal cancer, for exactly the same reason. Yet, it is now known, at last, that there is a specific germ of plant cancer, and the responsible bacterium itself is at this moment imprisoned in bottles at the Department of Agriculture. Does it not, then, seem likely that sooner or later an organism responsible for human cancer will be successfully isolated and identified?