304 CAUSE OF SECRETIONS. I' BOOK n. 



Hence it was inferred that the quantity of starch in the 

 Potato decreases in these periods ; an erroneous conclusion, 

 but one which of late has often been drawn. Yet it is obvious 

 that such per centage determinations only give the relative, 

 and not the absolute, quantity for either a plant or part of a 

 plant. De Candolle's statement, even if correct, shows no- 

 thing more than that the proportion of the weight of starch 

 to the whole weight of a Potato is successively that of 10, 

 14-!-, 17, &c., to 100, but whether this altered proportion 

 depends on the change of the contained starch or the dimi- 

 nution of other matter, is nowhere stated. It is far more 

 likely that in this the starch is neither formed nor destroyed, 

 but that the water contained in the Potato is lost by evapo- 

 ration, and is regained by absorption when the plants again 

 begin to grow." But if he thought De Candolle wrong, Pro- 

 fessor Schleiden should have produced some counter proof; 

 instead of which we have a mere opinion, very decidedly 

 given, but wholly unsupported by evidence, and contrary to 

 every one's experience. 



In the Beet-root the part most rich in sugar is that near 

 the lower end, where the earth prevents the light from pene- 

 trating ; if the above-ground portion is earthed up, we are 

 assured by M. Gaudichaud that the quantity of sugar then 

 is increased. In like manner in the Sugar cane it appears 

 that the lowest joints of the stem, most remote from the 

 leaves, are the richest in sugar, and vice versd. Whence 

 M. Gaudichaud concludes that sugar is not secreted in such 

 plants by their leaves. The facts just stated do not, however, 

 prove any such thing ; they only show that a secondary action 

 takes place in certain plants, in places far removed from 

 leaves, and that this action is facilitated by (or connected 

 with) the absence of light.* But the matter out of which 

 the sugar was obtained all derived its origin, in the first 



* Upon these phenomena M. Gaudichaud makes the following just remark : 

 " II y a dans la nature une physiologic, et une chimie physiologique ou chimie 

 naturelle, dont les phdnomenes s'accomplissent sous Faction de la vie et pour la 

 vie elle-meme ; chimie entierement distincte, a nos yeux, de celle qui traite et n'a 

 encore pu traiter que des corps inorganiques et des corps organises mourants, 

 ou entierement prive's de vie, qui tue et ne saurait rien animer, et que bien mal 

 a propos, selon nous, on d^core du titre de physiologie. 



