122 



MORPHOLOGY OP 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 mierosporangium, showing 

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

 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 600. 

 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 625. _D, later stage in first mitosis showing 

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

 shown in 0\ x 625. — After Guignard. 18 



by Frye 5<3 to occur regularly in Asclepias and allied genera ; by 

 Rosenberg 07 in Zostera; and Neottia nidus-avis is cited by 

 Goebel 16 (p. 368). 



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

 llel mill lienin in, Epilobium, Asclepias, and Lappa, only one 

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



