262 
PROFESSOR MACAIRE ON THE DIRECTION ASSUMED BY PLANTS. 
liquid which he supposes to be inferior in density to that inclosed in the cells. In the 
endosniose experiments it is usual to take liquids rather different in their specific 
gravities ; and it seems that if we admit that the sap contained in the cells of the 
upper part of the plant, where it has been already elaborated, may have a specific 
gravity sufficiently greater than the surrounding water to let it come in by endos- 
mose, it is not so easy to understand this difference of density from cell to cell as being 
sufficient not only to allow endosmose to take place, and still less to produce the 
enormous ascensional power which is admitted to exist in the sap. It occurred to 
me that the effects of endosmose in such a case might be ascertained by means of 
experiments. 
I took three glass tubes of unequal diameters, such as could be put one inside 
the other. One of the apertures of each tube was closed with a piece of bladder, and 
after a solution of sugar of 1‘13 specific gravity had been introduced into them, they 
were placed the one within the other : the last or largest tube was dipped in pure water. 
The height of the liquid in each tube was carefully ascertained, and the endosmose 
then observed. The liquid in the largest tube did, as usual, increase in bulk by the 
replenishing endosmose of the water outside of it, and the effect went on gradually 
increasing for several days. But during this time, the liquid of the two other tubes 
did not experience any change of level, the difference between the respective den- 
sities of the solutions they contained and the liquid of the larger tube not being 
sufficiently great to produce endosmose. This experiment, many times repeated, 
both with alcohol and with solutions of gum or sugar, always gave the same result, 
and seems to show that a succession of cells would not act otherwise. The trans- 
mission of a liquid from one to the other by way of endosmose either would not take 
place, or at all events would be too slow to account in any manner for the rapid 
ascent of the sap. 
In repeating Dutrochet’s experiments on the turgid state that the cellular tissue 
of plants takes in water, and employing for that effect coloured liquids, it occurred to 
me, that the absorbed liquor was not inside the cells themselves, but in the intercel- 
lular spaces, which accords with the rapidity of the result, which it would be impos- 
sible to understand if the liquid were to proceed from cell to cell and through their 
walls. 
It occurred to me also, that if endosmose was the only or principal agent of the 
ascension of the sap in plants, that is to say of vegetation, this phenomenon ought 
to be influenced by the two indispensable agents of vegetation, heat and light. As 
there is something rather mysterious in the phenomenon of endosmose, it was not 
impossible that such might be the fact. Dutrochet, from an experiment on the 
caecum of a fowl, concluded that a rise in the temperature increased both the 
rapidity and the quantity of endosmose. In his experiments on acids he even an- 
nounces having discovered that the temperature changes the direction of endosmose, 
which goes from the water towards the acid, or from the acid towards the water. 
