,^ THE DISCO\^ERY OF CANCER IX TLAXTS 



X. 



Gl 



with it. They finally succeeded in sep- 

 arating a white bacterio-organism found 

 in the tumors which they discovered 

 would produce the crown gall when in- 

 troduced into a healthy plant. This they 

 have named the Bacterium tumcfaciens, 

 or tumor-producing organism. 



Subsequent experiments showed that 

 the most uniform success followed ex- 

 periments upon young and rapidly grow- 

 ing plants, it being often possible to ob- 

 tain 100 per cent of infections. But 

 eight years passed before they were able 

 satisfactorily to stain the organism in the 

 tissues so that it could be demonstrated 

 under the microscope. 



Still further work was necessary be- 

 fore Dr. Smith was convinced that the 

 time had come when this disease could 

 be properly described as plant cancer. 



THE PLANT CANCER DISCOVERED 



These results have been announced in 

 two luminous bulletins of the Bureau of 

 Plant Industry, Kos. 213 and 255. con- 

 taining a series of admirable photo- 

 graphs and photo-micrographs, which 

 show the plant cancer in all its varia- 

 tions. 



With the aid of some of these photo- 

 graphs, we will follow Dr. Smith through 

 one of his experiments, showing how the 

 cancer is produced ; how it sends out 

 tumor-strands from the original point of 

 infection ; how secondary cancers de- 

 velop from these tumor-strands ; also the 

 dilTferent structure of primary and sec- 

 ondary leaf tumors, and finally we shall 

 see both the disturbance produced in the 

 normal cell structure and the Bacterium 

 tumcfaciens, which is responsible for the 

 trouble. 



In Plate I (page 54) we have one of 

 the Paris daisies, or margurites, which 

 served as the medium for very many im- 

 portant experiments. A sterilized needle 

 is taken and dipped into the culture con- 

 taining the bacteria, and one or more 

 small pricks are then made in the skin of 

 the plant. After a few days nodules ap- 

 pear, wdiich finally grow into the pri- 

 mary cancer, producing the malforma- 

 tions shown in this plant at the points 

 marked X, where the inoculations were 

 made. From this point the cancer be- 

 gins to throw out its roots or tumor- 



strands, which work their way up and 

 down the stem and into the leaves, throw- 

 ing ofif secondary cancers as they pass. 

 These secondary cancers can be plainly 

 seen at the points marked A and C, 

 where they have ruptured to the surface, 

 while a number of them, still buried in 

 the normal tissues, are visible along the 

 leaf E, with others at D. 



In the right-hand corner of the plate 

 there is a cross-section of the stem taken 

 at the point marked 1, which shows how 

 a large ' tumor-strand (marked S) ap- 

 pears to the naked eye. 



WHAT A TUMOR-STRAND IS 



This tumor-strand is of great impor- 

 tance in determining the cancerous na- 

 ture of the gall disease. In the Ency- 

 clopaedia Britannica, Dr. Louis Court- 

 land says : "A cancer follows a course 

 very different from that of an innocent 

 tumor. Its growth has no appointed ter- 

 mination, but continues with unabated 

 vigour until death ; moreover, it is more 

 rapid than that of the innocent tumours, 

 and so does not permit of the formation 

 of a capsule by the neighboring tissues. 

 In consequence such a tumour shows no 

 well-defined boundary, hut from its mar- 

 gin fine tendrils of cancer cells make 

 their zvay in all directions into the sur- 

 rounding parts, which gradually become 

 more and more involved in the process. 

 Thus a cancer of the breast will attack 

 both the skin covering it and the under- 

 lying muscle and bone ; a cancer of the 

 intestine will eat its way into the liver, 

 spleen and kidney, until these organs be- 

 come to a great extent replaced by can- 

 cer cells, and can no longer perform 

 their proper functions." 



In this tumor-strand, therefore, we 

 find just exactly what we should expect 

 to find in a plant sufifering from cancer. 

 The enormous rapidity with which plant 

 cancers may develop is shown on Plate 

 II, which exhibits two sugar-beets inocu- 

 lated by needle pricks with pure culture, 

 the photograph being made only two 

 months after the roots were infected. 



WH.\T CELLS LOOK LIKE 



We will now^ turn to Plate III and see 

 how the tumor-strand disturbs the nor- 

 mal cell structure. This plate shows a 



