14 CALIFOK.V/A ACADEMY OF SC/EyCES. [Proc. 3D Ser. 



certain, however, that its origin is not traceable to a single 

 cell. As the anther grows, the archesporial cells rapidly 

 divide in all directions and become distinguished by their 

 denser contents and larger nuclei (fig. 13) ; but even in the 

 later stages the boundary between the sporogenous cells 

 and those lying outside is not always perfectly clear. In 

 general, however, the two layers of cells lying within the 

 epidermis do not divide any further by periclinal walls, and 

 the inner one may be considered as a tapetum. The outer 

 cells later become much compressed by the growth of the 

 sporogenous tissue, and the inner layer almost absorbed 

 before the final division of the spore-mother-cells. Before 

 the spore-mother-cells separate, the inner envelope, or integu- 

 ment, has grown up beyond the apex of the anther, and the 

 cells of the upper part become enlarged, so that two thickened 

 lobes are formed, the whole, in section, closely resembling 

 the micropyle of an ovule (figs. 14, 15). The flower has a 

 short, thick stalk, and in the center is a vascular bundle, 

 which, like the other parts of the plant, shows in its earlier 

 stages a single row of short annular or spiral tracheids, 

 which are later destroyed by the rapid elongation of the 

 pedicel. 



{a) Development of the Pollen. — The spore-mother-cells, 

 previous to their separation (fig. 15), show the usual dense, 

 granular contents. The nucleus is of moderate size, with a 

 distinct but not specially large nucleolus. The individual 

 cells are decidedly elongated, and even after they separate 

 retain this form (figs. 17-21). Just before the first nuclear 

 division takes place, the nucleus appears larger than in the 

 cells which have not yet separated, and the protoplasm 

 presents a more or less definitely vacuolar appearance. 

 Probably the centrospheres are always present, but it must 

 be admitted that the observations made were by no means 

 conclusive. Owing to the granular nature of the cytoplasm 

 and the difficulty in differentiating these very elusive bodies, 

 the writer does not feel in a position to speak positively 

 about the matter, and must pass over the behavior of these 

 structures during the process of nuclear division. 



