miscellaneous: stimuli underlying tumor-formation 553 



of ammonia liberated in small quantity in a closed space, the 

 protoplasmic membranes of many cells of the leaf are paralyzed 

 and water escapes into the intercellular spaces, the evidence of 

 this being a fugitive mottling of the leaf, due to the substitution 

 of water for air in certain of the intercellular spaces. This 

 mottling due to escape of water into the spaces between the cells 

 can be produced in various other ways, e.g., by sulphur dioxid, 

 as O'Gara has shown, by chloroform, or simply by a minimum 

 freezing, as Harvey has shown. Usually within a half hour the 

 mottling of the cauliflower leaves due to slight exposure to vapor 

 of ammonia (Fig. 381), disappears and the plant again appears 

 to be normal, but it is not, since tumors immediately begin to de- 

 velop in the least mottled areas and within a few days are plainly 

 visible on the surface of the leaf (Fig. 365). Depending ap- 

 parently on the amount of the stimulus, or cell-paralysis, these 

 tumors are either hypertrophies or hyperplasias, just as they 

 are in frozen spots on the same plant and in the insect, nematode, 

 and myxomycete galls already referred to. This, at least, is the 

 way I would interpret it. If the karyokinetic mechanism of the 

 cell is paralyzed the hyaloplasm is certain to be more so and 

 in the end there will be an inflow of water with stretching of 

 the cell (hypertrophy) ; if on the contrary, only the protoplasmic 

 membrane is disturbed, with the returning influx of water and 

 foods the cell will divide repeatedly and a hyperplasia will result. 

 The irregular spotting of the leaves and correspondingly irregular 

 development of tumors depends clearly on the varying degree to 

 which stomata are open at the time of the exposure, since the 

 alkalin vapor enters the leaf through these minute openings. 

 In leaves with the stomata wide open there is always a consider- 

 able killing effect, similar to that shown in Fig. 374, whereas in 

 young leaves with the stomata closed or nearly closed only a 

 stimulating minimum of the poison enters and tumors result.^ 



1 To determine quickly the extent to which stomata are open in various areas 

 on the upper and under surface of young and old leaves at different times of day, the 

 surface may be painted with petrolatum, the irregular penetration of which corre- 

 sponds exactly to the irregular killing effects of excess of ammonia and of acids. 

 The writer stumbled on this method independently but apparently it was first 

 used by Emmy Stein {Ber. d.d. hot. Gea., 30 Bd. 1912, p. 66). 



