162 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



plastids in turn arise either from preexisting plastids or from chon- 

 driosomes. In very young pollen grains the reserve food consists 

 almost entirely of droplets of fat, and starch formation begins only 

 after the pollen grains have increased in size. 



WW 



A 



Fig. 100. Portions of pollen tubes of Lilium martagon showing behavior of "colored 

 bodies" inside generative cell and sperm cells, as seen in living condition. A, 

 generative cell in division, showing colored body at either end. B, enlarged view 

 of one end of generative cell, showing detail of colored body. C-E, stages in 

 division of generative cell. F, G, sperm cells, showing the colored bodies. (After 

 Kostriukova, 1939b.) 



Certain proteinaceous bodies have also been reported in pollen 

 grains and pollen tubes (Fig. 101), but their exact origin remains 

 unknown. They probably arise in plastids but soon become liber- 

 ated in the general cytoplasm of the pollen grain and pollen tube. 

 Most remarkable of all are the large transparent protein crystals of 

 Wormia suffruticosa (Paetow, 1931) (Fig. 99N), although these are 

 of a transitory nature and disappear during the later stages in the 

 maturation of the pollen grain. 



