122 



MORPHOLOGY OF ANGIOSPERMS 



the tetrads indiscriminately tetraliedral or bilateral, but fre- 

 quently the four spores are in a row. A tetrad consisting of 

 four spores in a row has also been found by Strasburger 5i and 



5 C75?1.0 n 



5 (,7 8 



Fig. 53. — Lilium Martagon. A. transverse section of young mierosporangium, showing 

 two nuclear mitotic figures in sporogenous cells and one in a hypodermal cell ; such 

 figures show 24 chromosomes, the sporophyte number; x 200. B. chromosomes of 

 a mitotic figure in the wall of a mierosporangium, showing 24 chromosomes; x 6<i0. 

 C, pollen mother-cell: polar view of the first mitosis, showing 12 chromosomes, the 

 gametophyte number, in the nuclear plate; the segments are double, one-half of 

 each segment will pass to each pole ; x »i25. A later stage in first mitosis showing 

 12 chromosomes, each chromosome representing one-half of one of the 12 segments 

 shown in C\ x 625. — After Guignard." 



by Frve 56 to occur regularly in Asclcpias and allied genera '< °Y 

 Rosenberg 57 in Zostera; and Neottia niJus-avis is cited by 

 Goebel 16 (p. 368). 



It has been claimed that in Zostera, Cyperaceae, Clematis, 

 Helianthemum, Epilobium, Asclepias, and Lappa, only one 

 microspore is formed by a mother-cell. In every case except 



