No. 454-] STUDIES ON THE PLANT CELL. 731 



genesis in the liighest type, Anthoceros (Davis, '99). This form 

 is exceedingly attractive for svich investigations because the 

 spore mother-cells may be found in all conditions upon the same 

 sporophyte. However, the small size of the nuclei and spindles 

 is a disadvantage. Just previous to the first mitosis the nucleus 

 becomes surrounded by a mesh of delicate fibrillse (kinoplasmic). 

 Later the nucleus takes an angular form, and the fibrillse are 

 found conspicuously at the prominent poles (Fig. 12 e). The 

 nuclear membrane breaks down and the fibers become arranged 

 to form a bipolar spindle (Fig. 12 f) without centrosomes or 

 centrospheres. There is a short period of rest after the first 

 mitosis, but no wall is formed between the two daughter nuclei. 

 The small spindles of the second mitosis (Fig. 12 g) are like-, 

 wise bipolar. They lie at right angles to one another and the 

 cell plates that are laid down determine, in part, the position of 

 the walls that are formed between the four granddaughter 

 nuclei and which divide the spore in a tripartite manner. These 

 cell plates are very small (Fig. 12 h and z), but they have been 

 observed in a favorable species of Anthoceros by Van Hook 

 ( : 00). It is not clear how these plates become extended to 

 the wall of the spore mother-cell unless (as suggested in Sec. H) 

 their edges make use of planes of vacuoles when the protoplasm 

 separates to develop the cleft between the four daughter cells. 

 The poles of the spindles in Anthoceros are flattened and entirely 

 free from structures that might be considered centrosomes. 



Other interesting events of sporogenesis in Anthoceros are 

 the division of the chromatophores and the nuclear condition 

 termed synapsis. The young spore mother-cell contains a single 

 large chromatophore. This increases greatly in size and becomes 

 filled with starch grains. The chromatophore divides succes- 

 sively into two and then four portions which arrange themselves 

 symmetrically in the cell with the nucleus in the center. The 

 mitoses then follow and the four daughter nuclei are distributed, 

 one for each chromatophore in the cell. This provision of four 

 chromatophores long before the mitoses in the cell seems very 

 remarkable (Davis, '99, p. 94 and 95). Synapsis is a condition 

 very common in the nucleus of spore mother-cells before divi- 

 sion. The chromatic material becomes gathered into a compact 



