PROFESSOR MACAIRE ON THE DIRECTION ASSUMED BY PLANTS. 
263 
according- as the thermometer is low or high. At all events he does not generalize 
this singular result, which, according to him, belongs only to the acids ; but as a great 
many saps have an acid reaction, the result ought to be, that, aecording to the state 
of the temperature in those cases, the sap should enter the tree or flow out of it : 
this seems to be in opposition to all known facts. 
In all the experiments I have tried, and they have been numerous, I have never 
been able to ascertain that heat had any apparent influence in promoting endosmose. 
It is obviously necessary to deduct the effect produced by the dilatation of the liquid 
by the caloric, or wait until it has returned to its previous temperature, before mea- 
suring its bulk. With this precaution, the quantity of water introduced into tubes 
perfectly similar and containing the same solution of sugar, was found to be exactly 
equal in the same time, though one of the tubes was maintained at a tempera- 
ture of 65° C. (149° Fahr.) and the other at 10° C. (50° Fahr.). The ascent of the 
liquids by endosmose proceeded at exactly the same rate when the tube was kept 
at a constant low temperature as when it was raueh more heated, and then brought 
back again to the usual temperature of the atmosphere. Heat does not appear to me 
to have any influence in increasing either the quantity or the rapidity of endosmose. 
Similar experiments were made, preserving for the endosmose apparatus the same 
temperature, but exposing one to the influence of light and keeping the other in 
complete darkness. The tubes and the liquids were absolutely similar, and there 
was no difference whatever found in the rapidity or quantity of the ascent of the 
liquid in the tube. When the same endosmose apparatus was exposed alternately 
to light and to darkness, the same decreasing rate of the endosmose was observed 
that would be seen in an apparatus constantly kept in darkness or in the light, 
and no special influence of light could be discovered. Thus, to give an instance 
of one of the numerous experiments performed, the mean rising of the liquid in an 
endosmose tube has been in lines, — 
In 
the light 
in 
darkness 
in 
light . 
in 
dark . 
< in 
light . 
in 
dark . 
in 
light . 
in 
dark . 
in 
light . 
Lines. 
3 
1*9 
1-8 
1-8 
17 
17 
1-2 
1 
07, &c. 
Many times repeated, and with various liquids, these experiments have always 
given the same results ; and I think I am entitled to conclude from them, that heat 
and light have no apparent influence on the endosmose phenomenon. 
There appears to me, from all these facts, very little probability that endosmose 
