162 The Botanical Gazette. [March, 
was drawn on to a far greater extent than the glycerine, the 
latter being thus protected. In case the dextrose was pres- 
ent in small quantities, it was totally consumed before the 
close of the experiment and the glycerine was then used until 
the close. Although dextrose was able to protect in great 
part the glycerine, still, even when present in abundance, it 
did not do so completely. 
When lactic acid took the place of glycerine, a similar gen- 
eral result was reached. 
In case acetic acid, in food value approximately equal 
to glycerine and lactic acid, was offered with dextrose, a dif- 
ferent result was reached. Although a poorer food than dex- 
trose, the consumption of acetic acid was large, in cases eX 
ceeding, in ratio to the quantity offered, that of the dextrose. 
Here, the better food did not protect the poorer from use nor 
did the poorer protect the better. Why acetic acid is thus 
consumed at the same time with the dextrose, is a question 
which the author does not attempt to answer. ggests, 
however, that it may be of special availability for the satis 
faction of some single function. The suggestion of the satis- 
faction of single functions does not receive full discussion but 
indicates interesting possibilities. 
When peptone took the place of dextrose in experiments 
similar to the above, very similar results were obtained. 
the whole, peptone protected the poorer food more com 
pletely than dextrose. 
By growing fungi in a mixture of dextro- and levo-gytt 
tartaric acids very interesting results were obtained. 
While Pasteur, in 1858, found the dextro-acid was used, 
leaving the solution levogyrate, Pfeffer found that while @ 
Majority of the forms used in his experiments acted similarly, 
almost as many showed no choice, using both kinds in pe 
quantities. One form, a bacterium, chose the left-hande 
acid, leaving the solution dextrogyrate. 
Pfeffer considers the causes influencing selection to be 
largely referable to plant regulation ard therefore, a functi® 
of irritability. 
n case of widely differing diosmotic properties, the ™* 
terial penetrating more rapidly than the other, though pera” 
no better food, will supply the demand to a larger deg 
The stimuli Prompting to a choice arise either a 
plant’s own products or from the substance offered. 
