376 BULLETIN OF THE 



nuclei again divide in the same manner, so that the wall of all four cells 

 is formed almost simultaneously, although the division of the parent 

 nucleus was by two successive steps. 



Still more remarkable is the abbreviation which prevails in the forma- 

 tion of spores in Anthoceros, and makrospores in Isoetes, for here the 

 spindle filaments are formed between two masses of protoplasm, while 

 the parent nucleus still retains itsform^ but the usual nuclear plates 

 are not produced. Each of the protoplasmic masses (potentially, though 

 not formally, a nucleus) again divides, without forming a nuclear plate, 

 and in each of the four masses arises a single nucleus, not, however, 

 until the parent nucleus, after remaining thus long, has finally dis- 

 appeared. These abbreviated forms of division serve as a possible expla- 

 nation of the phenomenon of free cell-formation. In the case of Picea 

 vulgaris, for example, after dissolution of the " Keimkern " (equivalent 

 to the nucleus of the first segmentation sphere in animals), normally 

 four cell nuclei arise simultaneously in the upper end of the " ^^^ " (p. 

 21). These exercise an influence on the surrounding protoplasm, which 

 is thus made to assume a radially striate appearance about the nuclei as 

 centres. The boundary of the four corresponding cells then makes its 

 appearance, and what is left of the substance of the egg-cell furnishes to 

 these four cells (or their descendants) albuminous matter. In the case 

 of another conifer (Ginko biloba) there are as many as thirty new nu- 

 clei, which simultaneously take the place of the primary nucleus, and 

 about these, as centres, all the protoplasmic contents are divided into a 

 corresponding number of cells. 



In the formation of free endosperm cells of Phaseolus multiflorus the 

 nucleus and cell make their appearance at the same time, — not the nu- 

 cleus first, as has usually been maintained, — the former in almost 

 punctiform size, the latter as a clear, circular zone surrounding the for- 

 mer. Both increase in size : the zone often exhibits a radiate arrange- 

 ment of protoplasmic particles about the nucleus as a centre. The 

 nucleus remains for some time homogeneous, and then several vacuoles 

 simultaneously make their appearance. The protoplasm of the cell 

 becomes reticulate ; the nucleus assumes an eccentric position ; the 

 protoplasm finally takes the form of a thin, granular mural layer, free 

 from vacuoles ; the cells, by their increase in size, come into mutual 

 contact ; and it is only then that a cellulose layer is to be discovered. 



The radial structure of the zone surrounding the nucleus in the case 

 of the *'Ei" of Ephedra — where the free cell-formation is much like 

 that of the last case — is particularly distinct, and the protoplasm of 



I 



