12 



ANNALS NEW YORK ACADEMY OF SCIENCES 



1 case 



3 cases 



18 cases 



119 cases 



174 cases 



198 cases 



84 cases 



20 cases 



(> cases 



1 case 



1 large spore, 



2 large spores nearly equal in size, 



3 spores of irregular sizes, 



4 spores of uniform sizes, 



4 spores of irregular sizes, 



5 spores of irregular sizes, 

 (> spores of irregular sizes, 



7 spores of irregular sizes. 



8 spores of irregular sizes, 



9 spores of irregular sizes, 



From such a survey it appears that the normal number of four spores 

 is formed from nearly one half of all pollen mother cells, hut that in 

 more than half of these cases the spores are irregular in size. In about 

 one-fifth of all the cases four spores of nearly uniform size are formed. 

 The omission of any division, which gives but one spore from a pollen 

 mother cell, occurs rarely. 



Variations in the Size of the Microspores 



The microspores have been especially studied in cytological prepara- 

 tions made from anthers that were about to dehisce. There is consider- 



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Photomicrograph of pollen grains In the anther shortly before anthesls, showing the 

 large proportion of undersized and shrivelled microspores. 



able variation in the size of the grains with all gradations between the 

 extremes. The mature dry grains are ovoid in Bhape with a conspicuous 



