126 



MORPHOLOGY OF ANGIOSPERMS 



O 



B 



but it was not absolutely certain that in case of the higher num- 

 bers all the microspores came from the same mother-cell. In 

 Hemerocallis fulva Strasburger 10 has counted nine microspores 

 f rom a single mother-cell ; and later Juel 33 and Fullmer 44 re- 

 ported six to eight in the same species. More recently Miss 

 Lyon 40 has found five or six microspores of equal size produced 

 by a single mother-cell of Euphorbia corollata. 



According to Wille, two microspores result from a failure 

 of the mother-cell to undergo the second division. When three 

 are formed, the first division is unequal, and only the larger 



cell divides. Five or 

 more microspores are 

 formed by subsequent 

 division of one or more 

 members of the tetrad. 



Strasburger, 10 Juel, 33 

 and Fullmer, 44 in their 

 study of Hemerocallis 

 fulva found an explana- 

 tion of the irregular 

 numbers. Strasburger 

 found that chromosomes 

 which fail to pass to 

 either pole at the first 

 mitosis give rise to small 

 microspores. Juel in his 

 more recent study con- 

 firms Strasburger, and 

 finds that even single 

 chromosomes which be- 

 come separated may divide and give rise to nuclei and organize 

 cells. Fullmer attributes the supernumerary microspores to the 

 division of one or more members of the tetrad. 



Perhaps no phase of plant cytology has received so much 

 attention as the nuclear divisions in the pollen mother-cell. It 

 is an interesting fact that the cytological characters of these two- 

 mitoses agree minutely with those in the megaspore mother- 

 cell. The pollen mother-cell can be positively identified by the 

 appearance of the synapsis stage (Fig. 54, J5), even before any 

 rounding off or separation takes place. While yet in the spirem 



Fio. 57. Variation in the arrangement of the spores 

 of a tetrad. A-C, Orchis mascula, x 380; after 

 WILLE." D-E, Typha latifolia, x 400 ; after 



SCHAFFNER. 34 



