1908] GATES— REDUCTION IN OENOTHERA 5 



shows that no line of distinction can be drawn between them and the 

 large body readily recognized as the nucleolus. They are then 

 smaller nucleoli, not differing essentially in origin from the single 

 larger body which is almost constantly present in the mother cell 

 during synapsis and prophase, but diverging from the latter some- 

 what in their later history. 



In the earliest stages studied, the young meristematic cells of the 

 anther primordia are very small (figs. 1, 2), and the tissues are wholly 

 undifferentiated, except the epidermal layer. Usually several smaller 

 nucleoli are present in each nucleus of the meristematic cells, in addi- 

 tion to the larger nucleolus. Compared with the cells of the anther 

 wall when they are no longer meristematic, the smaller nucleoli of 

 the former are about the size of the nucleoli of the latter, which are 

 approximately equal in size. There is nothing in the latter corre- 

 sponding to the larger nucleolus of the meristematic cells. Probably 

 afterward one of these nucleoli enlarges as the cell increases in size, 

 or it is possible that the nuclei of meristematic cells are always derived 

 from previous ones which already possess a large nucleolus. 



Chromatic staining bodies are also found closely appressed to the 

 nuclear membrane in all the meristematic cells (figs. 1, 2). This 

 tendency for chromatic material to accumulate on the nuclear walls 

 gives these nuclei a characteristic appearance. These bodies often 

 appear like a thickening of the membrane itself. 



At the next stage studied many cell divisions have taken place, 

 and the sporogenous, tapetal, and wall tissues have been differentiated. 

 The sporogenous cells have increased enormously in size, and form 

 a single row in longitudinal section down the center of the anther, the 

 walls of these cells being especially thickened and distinct (fig. 3). 

 The cells of the surrounding tapetal layer have also increased greatly 

 in size and are distinctly marked off from the sporogenous row. In 

 the sporogenous cells the nuclei (fig. 4), though much increased in 

 size, have not increased in proportion to the cytoplasm. The large 

 nucleolus, much larger than in the earlier stage, is now a conspicuous 

 object in the nucleus. Smaller nucleolar bodies are almost invariably 

 present, but masses are no longer found attached to the nuclear 

 membrane. (The characteristic masses, however, may remain for 

 some time attached to the nuclear walls of the tapetal cells) . 



