58 ANATOMY AND PHYSIOLOGY OF 



in comparison -with tlie parent-cell, and stand in no connexion, or, 

 at leastj not a necessary one, with the walls of the latter. 



In the Phanerogamia, free cell-formation occurs only in the 

 embryo-sac, in which both the rudiment of the embryo (the em- 

 bryonal vesicle) and the cells of the endosperm originate in this 

 way ; in the Cryptogamia it occnrs only in the formation of spores 

 in the Lichens, and some of the Algse and Fungi. 



The formation of free cells is usually preceded by the produc- 

 tion of nuclei. In this case more or less abundant accumulation 

 of protoplasm in the parent-cell forms the first sign of the second- 

 ary cells. This sometimes fills up the cavity of the parent- cell, 

 e. ^ , in the parent-cells of the spores of the Lichens, Pezizm, &c., 

 sometimes it occurs in relatively small quantity under the form 

 of cloudy masses not sharply defined, and of currents, as is usual 

 in the embryo-sac (pi 1, fig. 12, s). In this protoplasm are formed 

 isolated points of concentration in the form of more or less trans- 

 parent nuclei, around which accumulates ayariable portion of the 

 burrounding protoplasm, originally exhibiting no decided outline, 

 subsequently clearly defined by the formation of a primordial 

 utricle over the surface, which is rapidly followed by the produc- 

 tion of a cellulose membrane enclosing the whole nitrogenous 

 contents (pi. 1, figs. 13, h ; 14, h), 



Ohsem. To Schleiden belongs the merit of dibcovermg free cell-formatioii 

 and the depeadaiice in which the origin of a cell stands to the formation 

 of a nucleus ; but he was led by this discovery to the misconception that 

 this was the only mode of formation of the cell occxuTing in natiu*e. In 

 accordance with thib hypothesis, the cells which were formed in other cells 

 would always be much smaller than the parent-cells, and would gradually 

 expand imtil they filled up the cavity of the parent-cells, and their walls 

 came into contact. But as the whole process could not take place in 

 cells which contain granular structures, such as chlorophyll or starch gra- 

 nules, or the like, without the displacement of these structiu'es, and yet in 

 a cell of that kind in which division occurs, all these structures are still 

 present after the division, Schleiden invented an hypothesis to explain the 

 ckcmnstance, namely, that these structures in the cavity of the parent- 

 cell were dissolved outside the secondary ceU, and formed a-new inside it. 

 But as nothing of this process can be observed hi nature, it alone suffices 

 to refute the doctx'me of the universality of free cell-formation. Even 

 when quite recently, in consequence of Nagelfs observations, Schleiden 

 {"Grundz." 3rd ed. i. 213) can no longer deny that a division of cells does 

 occur, still he is far from acknowledging the universal diffiision of this 

 process, since he only refers to the older notion, retracted by Hkgeli 

 himself, that this mode of formation occurs in the Pbanerogamia or in 

 the special parent-cells of the pollen-grains, and altogether ignores the 

 fact that llTageh and others have shewn this to be the mode of formation 

 of all cells except those originating in the embryo-sac; consequently, 

 Schleiden still ascribes to free cell-formation an influence on the develop- 

 ment of the plant which by no means belongs to it. When he states 

 that the cells are developed in this way in the embiyonal vesicle, this is 



