Oenothera Lata. 



409 



of grains, about 70% large normal grains,^ the rest being 

 small grains poor in protoplasm. The pollen of 0. lata 

 on the other hand consists of crumpled, distorted grains 

 which form every conceivable transition between abso- 

 lutely empty sacks and apparently normally developed 

 grains. But the empty ones and the almost empty ones 

 are in the majority ; the apparently well developed ones 

 occurring only sparingly amongst them. Moreover the 

 viscin threads, which in O. Lamar ckiana connect all the 

 pollen-grains together so that 

 they form a sticky mass, appear 

 to be absent. The open an- 

 thers feel dry and if they are 

 touched with the finger, bits 

 of sticky masses of pollen do 

 not adhere to it. 



If we follow the develop- 

 ment of the anthers in O. lata 

 in a series of buds of increas- 

 ing size we find that develop- 

 ment is normal up to about the 

 stage of tetrad - formation. 

 Shortly after this stage disso- 

 lution of the tapetum takes 

 place and there are found floating in the lumen, besides 

 apparently normally developed tetrahedral pollen grains, 

 some quite round, others invaginated on one side. 



I devoted a great deal of time in 1894 to trying to 

 fertilize O. lata with its own pollen, trusting that the 

 few apparently good pollen grains which I had found 

 would be able to effect fertilization. I plastered as much 



Fig. 90. Oenothera lata. 

 Transverse section of an 

 anther, showing the large 

 cells of the tapetum. After 

 J, PoHL, Oesterr. Bot. Zeit- 

 schrift, 1895, Plate 10, Fig. 

 28. 



^Figured by Luerssen" in Pringsheim's Jahrhiich., Vol. VII, pp. 

 35-42, and Plate IV, Figs. 1-14 (Pollen of Oenothera biennis). 



