122 



MORPHOLOGY OF ANGIOSPERMS 



the tetrads indiscriminately tetrahedral 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 54 and 



FIG. 53. Lilium Martagon. A, transverse section of young microsporangium, 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 microsporangium, showing 24 chromosomes ; x 600. 

 (7, 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 625. /), 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 Frye 56 to occur regularly in Asclepias and allied genera ; by 

 Rosenberg 57 in Zostera ; and Neottia nidus-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 



