502 BACTERIAL DISEASES OF PLANTS 



E. Schilling, published on the same subject, having repeated 

 and expanded Wisniewski's experiments with similar results. 

 The \mter has also experimented on a number of plants, fig, mul- 

 berry, olive, begonia, ginkgo, etc. (Figs. 385A, 386) using 

 Squibb's petrolatum. As soon as the lenticels are obstructed, 

 gas interchange, i.e., inflow of air and outflow of carbon diox- 

 ide and vapor of water, ceases, or at least is greatly re- 

 stricted, and following this (in susceptible species, but not in 

 ginkgo) the cells under the lenticels at once begin to divide and 

 a considerable cushion of cells (hyperplasia) may develop 

 (Figs. 3855, and 387 to 389). 



Earlier than this it was known that the lenticels of potato 

 tubers frequently proliferate in very moist earth (Sorauer), 

 and also that the cut surface of potato tubers may proliferate. 

 Fig. 390 shows proliferations that appeared on a pared sterile 

 block of raw potato sealed into a test tube some months earlier 

 by Mr. Shapovalov, who gave it to me thinking it might be 

 crown gall. His experiments were for another purpose and these 

 growths occurred in one of his check tubes. We could find 

 no organisms in the tissues, either with the microscope or by 

 means of agar-poured plates. Their internal structure (Fig, 

 391) is a twisted vascular hyperplasia not unlike crown gall. 

 I tried to duplicate this in an atmosphere of nitrogen but only 

 succeeded in asphyxiating the tissues. It would, I believe, 

 be easy to get it with sensitive tubers and exactly the right 

 reduction of air space or of oxygen. Possibly it is an abortive 

 effort on the part of the flesh of the potato to reproduce the 

 whole plant. 



Since the preceding paragraph was written I have repeated 

 the experiments (spring of 1919) with pared blocks of raw 

 potatoes sealed into a moist, confined air-space and have verified 

 my prediction, as may be seen from Fig. 392. The blocks, 

 which were some of those already referred to as in cotton- 



FiG. 377. — Structure of small and large tumor on cauliflower leaf sprayed 

 with Koo formic acid water. From unstained water mounts: (1) Weaker 

 stimulus (stomata less open). (2) Edge of a large outgrowth. The whole tumor 

 is about four times the length of the part here shown. Both X 130 circa (8 mm., 

 4 oc, and bellows at 35). 



