322 BOTANICAL GAZETTE [OCTOBER 
Tropic responses.—In working out the phototropic responses of Avena 
sativa, Ar1sz® believes he has shown that the terms reaction time, presenta- 
tion time, threshold of stimulation, etc., do not represent any well-determined 
end points in tropic responses. Quotations from his paper present his con- 
clusions: ‘Each quantity of energy reacts on the plant and is expressed by a 
curvature of definite maximum strength.” ‘If we once more trace how far 
the above investigations influence our conception of the process of stimula- 
tion, it is clear that the similarity to physico-chemical processes becomes 
more and more marked. The existence of a threshold of stimulation can no 
longer be maintained, for not only is each quantity of energy perceived, but it 
is clear now that a reaction will always take place. The time which inter- 
venes between the application of the stimulus and the beginning of the curva- 
ture, the ‘reaction time,’ was found to be experimentally undeterminable. 
Thus the latter cannot serve as a measure of sensitivenesss.” 
We are urged, then, in this stronghold of stimulus physiology (tropisms), 
to abandon the stimulus conception for the physico-chemical. 
had earlier urged such a shift of viewpoint in the study of metabolic processes 
of plants.—WILLIAM CROCKER. 
The cytology of rice.—Since closely related species or even races of a 
given species may show differences in chromosome characters, several races 
of rice (Oryza sativa) were selected by Kuwapa™ for a cytological study. 
Just before synapsis in the pollen mother cell, a number of chromatin masses, 
about equal to the diploid number of checmceatsies: are found scattered 
throughout the nuclear cavity. The masses, which are constantly paired, 
stretch out into double threads, which remain double during synapsis, but fuse 
after the synaptic stage is past. Soon after synapsis, the single thread arising 
from the fusion again becomes double and segments into 12 bivalent chro- 
mosomes, or gemini, and throughout the prophases the two parts of the bivalent 
chromosomes remain in parallel association, while they become shorter and 
thicker. Even in the homotypic division paired chromosomes, forming pseU- 
dogemini, occur. In the diploid generation the chromosomes are always 
paired and the number is 24. The development of the embryo sac presents 
nothing unusual. There are at first three antipodals, but, as in other Grami- 
neae, the number becomes much larger at a later stage in the development.— 
CHARLES J. CHAMBERLAIN. 
Physics of transpiration —RENNER™ has already shown that in still air 
evaporation from surfaces of like shape but different size varies more nearly 
~ se W. H., On the connection between stimulus and effect in phototropic 
curvatures of weioliihiens of Heed sativa, Reprint from Proc. Konink. Akad. We 
tensch. saab March 25, 1 
™ Kuwaba, boise A eee study of Oryza sativa L. Bot. Mag. Tokyo 
24:267-281. pl. 8. 
™ Rev. in Bor. Cc 512156. 1grt. 
