222 PHYSIOLOGICAL BOTANY. 



lopment of cells. The investigations exhibit a depth of 

 research, which commences with the very earliest origin 

 of the plant, and in this respect they are very valuable. 

 First, Mohl, to whom we are indebted for most of our 

 knowledge on this point, has published : 



Remarks on the Structure of the Vegetable Cell, in the 

 Botanische Zeitung. Edited by H. VON MOHL and L. 

 VON SCHLECHTENDAL. Berlin, 1844, p. 15 et seq., and 

 p. 273 et seq. He was led to these researches by 

 Hartig's investigations upon the structure of cells, and 

 his assumption of their possessing a more internal mem- 

 brane which lines their interior, and which he deno- 

 minated a Ptychode. "If we examine a first year's 

 shoot of a tree, or the stem of an annual plant, which, 

 before the completion of its growth, has been immersed 

 in spirit and kept in it for some time, we find in all 

 those cells and vessels, the secondary layers of which 

 have not yet attained their full development, an inner 

 membrane, which is remarkably distinct from the other 

 membranes of the cell. This membrane forms a per- 

 fectly closed, cell-like, thin-walled vesicle, which in the 

 fresh plant is closely applied to the inner wall of the cell, 

 and therefore escapes observation ; whilst in specimens 

 which have been preserved in spirit, it is contracted, and 

 more or less detached from the wall of the cell/' He 

 calls this cell-like vesicle the primordial utricle, and found 

 it in a number of Dicotyledonous plants, as, e. g, in 

 JSambucus ebulus, Ficus carica, Pinus sylvestris, Asclepias 

 Syriaca, Hoya carnosa, Euphorbia Canariensis, Caput 

 Medusa, &c. In the Monocotyledons, he detected it in 

 the apex of the stem and of the root. But this utricle 

 can be seen by a shorter method than that of keeping 

 the portions of the plants for a long time in spirit. In 

 general, the preparation need only be exposed to the 

 action of nitric or hydrochloric acid for a few minutes ; if 

 the acid be then neutralized with ammonia, and the pre- 

 paration be coloured by iodine, the primordial utricle is 



