48 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



Drosera, Elodea, Typha, Furcraea, and several members of the Eri- 

 caceae, Apocynaceae, Asclepiadaceae, Juncaceae, and Orchidaceae. 

 In the Mimosaceae there are larger units composed of 8 to 64 cells, 

 and in a number of genera belonging to the Asclepiadaceae all the 

 microspores in a sporangium remain together to form a single mass 

 called the pollinium. The family Orchidaceae is especially interest- 

 ing in this connection (see Swamy, 1948). In some genera, such as 

 Cypripedium and Vanilla, the microspores separate from one another 

 and become free. In Pogonia the four cells of a tetrad adhere and 

 form a compound pollen grain. In the tribes Ophrydeae and Neot- 

 tieae this tendency is carried further and the compound grains are 

 themselves held together in small units known as massulae. Fi- 

 nally, in Coelogyne and Pholidota all the microspore mother cells and 

 their derivatives remain together and continue their development 

 as a single unit. 



References 



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 Beer, R. 1906. On the development of the pollen grain and anther of some 



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 Billings, F. H. 1932. Microsporogenesis in Phoradendron. Ann. Bot. 46: 979- 



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 Boehm, K. 1931. Embryologische Untersuchungen an Zingiberaceen. Planta 



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 Bonnet, F. 1912. Recherches sur revolution des cellules nourricieres du pollen 



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