gtr} CURRENT LITERATURE 239 
Evans thinks that a vigorous apical cell exercises an inhibitory action 
on the production of gemmae, and that when the apical cell is suppressed, or 
its activity lessened, gemmae are able to form. He says: 
Just why the normal activities of the apical region are lessened in these cases 
and finally brought to an end, is by no means clear. In some instances the result is 
perhaps due to poor nutrition, bringing about an enfeeblement of the whole plant; but 
this cannot be the effective cause in all cases, because a limitation of growth often 
takes place in plants which are robust. Under these circumstances the plant is prob- 
ably able to control the apical growth, perhaps by diverting the currents of food to 
other regions. Apparently something of the same sort takes place in such species as 
M. dichotoma, where the growth of the g iparous branch conti ¢ Se er 
period. The power of the plant to regulate the distribution of the nutritive materials, 
and thus to weaken or destroy the inhibitory influence exerted by the apical region 
upon the cells capable of producing gemmae, may be considered a specific character. 
It seems possible that the production of gemmae may rather be due to 
the influence of some external factor than to an internal self-regulating mechan- 
‘sm; and it is possible by experiment to determine what this factor may be.— 
W 
. J. G.“Lanp 
Presentation time.—RUuTGERS,” working in WENT’s laboratory at Utrecht, 
has studied the rélation of temperature to geotropic presentation time in the 
etiolated seedlings of Avena. He believes that VAN’r Horr’s law of speed of 
reaction for temperature holds from 5° to 30° C. with a coefficient of about 
2.6 for every rise of 10°. From o° to 10° the coefficient is 6.8. RUTGERS 
attributes this high coefficient to the effect of low temperature on growth. 
From 25° to 35° the coefficient is 0.93, and for higher temperatures still lower. 
The time of previous warming (varying 1 to 24 hours) has no effect up to 25°; 
Sut at 30° its effect is marked. At the latter temperature one hour’s warming 
8ives a presentation time of 3.5 min.; while 12 to 24 hours gives 1.66 minutes. 
These results do not agree with those of BAcH." It is certainly interesting, if 
true, that this chemical law applies to this supposedly complex process of per- 
ception as BLACKMAN” has shown it to apply in photosynthesis, and KuyPer’ 
m respiration, and various other workers in other processes. 2 
Serious criticism can be offered against RuTGERS’ methods and his dis- 
“ussion of literature. So far as his description of methods tells, he seems to 
(Saracen ee 
" Rurcers, A. A. L., The influence of temperature on the presentation time in 
ecotropism. English reprint from the Proc. Konink. Akad. Wetensch. Amsterdam. 
Oct. 29, Igto, 
: "Bach, H., Ueber die Abhiingigkeit der geotropischen Priisentation und Reak- 
Uonzeit von verschiedenen Aussenbedingungen. Jahrb. Wiss. Bot. 44:57-123- 1907- 
. > BLackman, F. F., Optima and limiting factors. Annals of Botany 19: 281- 
95. I905, 
* Bor. Gazetre 50: 233-234. 1910. 
