10 



INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



than in cryptogams, the actual demonstration did not come until a 

 few years later, no doubt because of the technical difficulties in 

 making any direct observations on the embryo sac, which is sur- 

 rounded by the opaque tissues of the nucellus and the integuments. 



Fig. 7. Stages in formation of microspore tetrads in Tradescantia. {After Hof- 

 meister, 1848; reproduced from Sharp, 1943.) 



Discovery of the Nature and Development of Male and Female 

 Gametophytes. Among early students of the development of pollen, 

 Hofmeister (1848) presented some surprisingly good illustrations of 



A B C D E F G 



Fig. 8. Development of male gametophyte of Tradescantia virginica. (After 

 Elfving, 1879.) 



the process of tetrad formation (Fig. 7), and Reichenbach, Hartig 

 and several other workers noted the presence of two nuclei in whole 

 mounts of the mature pollen grains of several angiosperms. Stras- 

 burger (1877) and his pupil Elfving (1879) extended these observa- 

 tions to cover several families and demonstrated the widespread 

 occurrence of the binucleate condition in pollen grains (Fig. 8). 



