340 H. S. DAVIS 



two sporoblasts are entirely distinct, and are often quite widely 

 separated. 



The later history of each sporoblast is the same, although 

 one usually lags a little behind the other in development. The 

 two smaller cells divide by mitosis, one usually a little after the 

 other (figs. 29, 33 and 34) forming sporoblasts with five cells, 

 usually lying in approximately the same plane and arranged 

 in a definite manner (figs. 30, 31, 35 and 36). The division in 

 this case is unequal, one of the daughter cells from each mother 

 cell being slightly larger than the other. These two cells later 

 form the capsulogenous cells which give rise to the polar capsules ; 

 the two adjoining smaller cells fuse to form the sporoplasm, while 

 the large cell at the end opposite the capsulogenous cells, 

 divides by amitosis into cells which later form the valves of the 

 sporocyst. In this division the nucleolus divides first, after which 

 the nucleus divides by a simple constriction (figs. 37 and 38). 

 Thus in each three-celled sporoblast the larger of the three cells 

 is destined to produce the parietal cells which form the valves 

 of the sporocyst, while each of the smaller cells will give rise to 

 one of the capsulogenous cells and one of the sporoplasm cells. 



Up to this time the resting nuclei show a similar structure 

 throughout the different stages, but shortly after the division 

 of the sporoblast into six cells the nuclei present a quite different 

 appearance (figs. 39 and 40). Definite nucleoli are no longer 

 to be distinguished, but are probably represented by several 

 deeply staining masses closely apposed to the nuclear mem- 

 brane. These masses are probably composed chiefly of chroma- 

 tin, the achromatic part of the nucleolus having disintegrated. 

 Throughout this and later stages there is a marked tendency in 

 all the nuclei for the chromatin to collect in larger and larger 

 masses. 



At this time there is also a general rearrangement of the cells 

 in each sporoblast, each cell assuming the position relative to 

 the others which it occupies in the mature spore. During the 

 formation of the spore all the nuclei decrease in size and stain 

 more deeply as a result of the concentration of the chromatin 

 in larger masses. The two parietal cells become flattened and 



