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THE NATIONAL GEOGRAPHIC MAGAZINE 



typical cell formation in the stem of a 

 plant as it appears in a cross-section or 

 looking down upon it from above. This 

 is a photo-micrograph, and the tiny cells 

 have been magnified until, taken collec- 

 tively, they look like a cobblestone pave- 

 ment; but we can now see how the cells 

 look when they are subject to both nor- 

 mal and abnormal stimulation. The 

 ^reat majority of the cells shown here 

 are behaving quite normally, but in the 

 <;enter of the picture, where the large 

 pith-cells join the smaller wood-cells, we 

 notice a little group of cells which seem 

 to be different from the others and to be 

 forming a little circular colony of their 

 own. These are the cells which, under 

 the stimulus of the cancer bacillus, form 

 the tumor-strand. 



Just how abnormally these cells are 

 Tjehaving will be immediately apparent 

 when we view a tumor-strand in longi- 

 tudinal section or in a front view as 

 ^iven in Plate IV. Here the cells in the 

 tumor-strand, which is shown in the cen- 

 ter of the plate and looks not unlike a 

 sweetbread, have a markedly different 

 appearance from those of the normal 

 tissue surrounding them. The effect of 

 their continued abnormal growth is 

 shown in Plate V, where a young tumor 

 is developing, while a more detailed pho- 

 tograph of a cross-section of a tumor- 

 strand lying in the midst of less abnor- 

 mal cells is shown on Plate VI. 



TH© NUCLEUS AND ITS FUNCTION 



This is a particularly interesting plate, 

 as it shows that the tumor-strand, just 

 like many human cancers, has a strong 

 affinity for the stain used upon the mi- 

 croscope slide, and this shows especially 

 quite dark. A series of small black spots 

 at the edges of the strand, which appear 

 will also be observed, very numerous in 

 the cells in the tumor-strand and ap- 

 pearing at intervals in a few cells on 

 other parts of the plate. These spots are 

 the nuclei or points from which prolif- 

 eration starts, and the superabundant 

 proliferation in the tumor-strand, due to 

 the stimulation of the parasite, can be 

 easily seen. 



An enlargement of the tumor-strand 

 area is given in Plate VII, which affords 

 a much clearer view of the nuclei. It 



will be observed that these points of pro- 

 liferation are distributed all over the 

 tumor-strand area, but are especially 

 numerous at the edges. 



Plate VIII shows a cross-section of 

 the stem of a daisy plant between the 

 primary and secondary tumors. The 

 tumor-strand occurs at the point x, and 

 the rest of the stem is quite normal ex- 

 cept for a slight thickening of the ring 

 of wood-cells at the point nearest the 

 tumor-strand. 



An enlargement of this tumor-strand 

 and the surrounding cells appears in 

 Plate IX, the tumor-strand being at the 

 junction of the small wood-cells above 

 and the larger pith-cells below. Here in 

 the tumor-strand we have the cells "dis- 

 placed from their normal relationship," 

 referred to in Cohnheim's hypotheses (see 

 p. 55), the pitted portion bemg vessels 

 (trachids) which have developed out of 

 place and still contain nuclei which are 

 absent from these vessels when fully de- 

 veloped. They also show, by their feeble 

 staining, that they are still in process of 

 of development, as adult vessels of this 

 type usually stain heavily. 



HOW PI.ANT CANCI^R DESTROYS TISSUE! 



A cross-section of a leaf stalk in which 

 a tumor has developed is shown in Plate 

 X. The ravages of the cancer can be ap- 

 preciated when we realize that the light- 

 colored cells at the top and left are all 

 that is left of the normal tissue. This is 

 a secondary tumor developed from a 

 tumor-strand which has pushed its way 

 up from a primary tumor situated on the 

 stem below, and consequently it has an 

 imperfect stem structure, consisting of a 

 central tumor-strand, which takes the 

 place normally occupied by the pith. 

 From it radiate in all directions woody 

 plates (the dark rays in the picture), 

 separated by enlarged pith rays (the light 

 rays), the whole being inclosed by a ring 

 of bark cells. The great excess of soft 

 cells leading to rapid decay and the ab- 

 sence of pith are the chief differences 

 between this and a normal stem. 



The very striking contrast between 

 such a secondary leaf tumor and a pri- 

 mary leaf tumor can be seen in Plate XI, 

 which is a cross-section of a primary 

 leaf tumor produced from a pure culture 



