158 BOTANICAL GAZETTE [AUGUST 
who seems to have ascribed phototropism in animals to the same fundamental — ‘ 
cause, though he thinks of the reactive pull rather than pressure. Utilizing — 
the figures calculated by Maxweti (1873) and recently determined experi- — 
mentally by NicHors and HULt,34 the pressure on a cell .or™™ square in full — 
sunlight would scarcely amount to 7X10~* milligram! To believe that a plant 
cell could discriminate between 0 and .000,000,000,07™ pressure (i. ¢, of 
darkness and of full sunlight) makes a severe test of one’s credulity; but when one — 
remembers that some plants discriminate between darkness and the light of one 
candle at a distance of 50™, and that the phototropic optimum of Vicia lies at 
3 candles, the reason simply balks at any possibility of the perception of such 
differences of pressure. 
Rapt, who has enunciated this idea regarding phototropism in animals,® 
and who endeavored unsuccessfully to test it experimentally with them, has 
turned to seedlings for confirmation. In a late paper’s he endeavors to minimize” 
the objection grounded on the minuteness of the energy involved (which o— 
absolutely conclusive against the hypothesis), and describes briefly a —_ of 
experiments in which he hung seedlings horizontally in a moist chamber by 2 
cocoon filament, so that they were poised at right angles to light admitted through 
a slit, while control seedlings were fastened in a like position. He then - 
whether or not the free ones were caused to rotate, directing their apices toward 
the light. Arguing that according to the extent of such rotation any curvatute 
they might also attain would be less than in the fixed controls, he interprets — 
51 results as giving 39 cases in support of his hypothesis and 12 against it ae 
sources of error both in experimentation and interpretation are s0 ea 
and the results are so inharmonious as to leave the matter still in statu quo. 
author recognizes the inconclusiveness of his results, but thinks them s iggestive- 
ARB, 
M ‘ : ut forth by Dr. 
“UCH HAS BEEN written regarding the mycoplasm theory Pp exter 
JaKos ERIksson, of Sweden, to account for outbreaks of wheat rust whe 
. . . 7 i le. ie! 
nal infection from aecidiospores or uredospores is presumably Imp der to set 
recent articles’ ErrKsson gave a concise statement of his position, 1n 0” of his 
right his critics and opponents in regard to the fundamental conception 
ry 
a first instalment of his histological studies which form the soli 
theory. e publishing | 
He has now laid the botanical public under a debt of gratitude oe of his . 
ing is 
theory, and by illustrating them with excellent colored plates.*” | 
34 Physical Review 17: 10r. 1903. Licht: Flora 93° 
35 Rabi, E., Ueber die Anziehung der Organismen durch das : 
167-178. 1904. | 
3° Archiv fiir Botanik 1:1 39-146. Getreiderost 
Kongl+ 
: T 
37 ERIKsson, J. and TISCHLER, G., Ueber das vegetative La ae 
pilze. I. Puccinia glumarum in der heranwachsenden WeizenP 
Svensk. Wet. Akad. Handl. 37:—. [no. 6. pp. 19-] pls. 3- 1994 
