324 Theory of Cell-formation [BOOK n. 



two spots, says Schleiden, in the plant, where the formation of 

 new organisation may be most easily and most certainly 

 observed, the embryo-sac and the end of the pollen-tube, in 

 the latter of which, according to his theory of fertilisation, the 

 first cells of the embryo are supposed to be formed, but where 

 in fact no cells are formed. At both spots small granules soon 

 arise in the gum-mucilage, which, before homogeneous, now be- 

 comes turbid, and then single larger and more sharply defined 

 granules, the nucleoli, appear. Soon after, the cytoblasts 

 are seen as granular coagulations from the granular mass ; 

 they grow considerably in this free condition, but as soon as 

 they have reached their full size, a delicate transparent vesicle 

 is formed upon them ; this is the young cell, which at first 

 presents the appearance of a very flat segment of a sphere, 

 whose plane side is formed by the cytoblast, the convex by the 

 young cell (the cell-membrane), which rests upon the cytoblast 

 as a watch-glass on a watch. Gradually the vesicle becomes 

 larger and of firmer consistence, and now the whole of the wall, 

 except where the cytoblast forms part of it, consists of a jelly. 

 By-and-bye the cell grows beyond the edge of the cytoblast 

 and rapidly becomes so large that the latter appears only as a 

 small body inclosed in one of the side walls. The shape of 

 the cell becomes more regular with advancing growth and 

 under the pressure of adjoining cells, and often passes into that 

 of a rhombododecahedron, which Kieser for reasons drawn 

 from the nature-philosophy assumed to be the fundamental 

 form. It is only after the resorption of the cytoblast that the 

 formation of secondary deposits on the inner surface of the 

 cell-wall commences, though some exceptional cases are 

 adduced. Schleiden thinks (p. 148) that he may assume that 

 the process here described is the general law of formation of 

 vegetative cell-tissue in Phanerogams. He adds particularly 

 that the cytoblast can never lie free inside the cell, but is 

 always enclosed in a duplication of the cell-wall, and he thinks 

 that it is an absolute law that every cell, except perhaps in 



