620 



PATTERNS AND PROBLEMS OF DEVELOPMENT 



filament, and also figures in which the two plane walls of successive fila- 

 ment cells diverge toward the same side and the nuclei are on the side 

 where the walls are farthest apart. The blepharoplast makes its appear- 

 ance adjoining the transverse cell wall toward the base of the filament, and 

 spermatozoids develop with the flagellate end also toward the base, sug- 

 gesting orientation of the pattern in relation to some factor in the fila- 

 ment as a whole, perhaps a gradient of some sort. 



Spiral spermatozoid pattern is characteristic of bryophytes and pterido- 

 phytes and develops as elongation and spiral coiling, first of the blepharo- 

 plast, then of the nucleus. In certain of these forms what may be called 



Fig. 197, A-E. — Male gametes of plants. A, pollen grain; B, section of developing sperma- 

 tozoid of Cycas revoluta (after Ikeno, 1898) ; C, spermatozoid of the cycad Zamia (from Webber, 

 1901); D, male nucleus of the sunflower Helianthiis (from Nawaschin, 1900); E, male nucleus of 

 Silphium (from IMerrell, 1900). 



the "polar axis," that is, the axis about which the spiral coiling occurs, 

 coincides in direction with the axis of the final mitotic spindle, the 

 blepharoplast before elongation being at the pole of the spindle. For ex- 

 ample, in Equisetum (Sharp, 191 2) the two sister spermatids of Figure 196, 

 B, evidently possess an axiate pattern in relation to each other, and the 

 later spiral coiling of blepharoplast and nucleus is about this axis (Fig. 

 196, C), resulting in the spermatozoid (Fig. 196, D). Spermatozoid de- 

 velopment in the fern Nephr odium (Fig. 196, £) is apparently very similar 

 (Yamanouchi, 1908). In the cycads — a group related, on the one hand, 

 to pteridophytes and, on the other, to spermatophytes — spirally ciliated 

 spermatozoids also develop. The cycad pollen grain (Fig. 197, A) shows 

 a definite axiate pattern, consisting of three cells, two representing the 



