82 



MORPHOLOGY OF GYMNOSPERMS 



3, The gametophytes 



In his examination of pollen grains, Wieland (22) discovered 

 appearances of cell structure, but it was not determined whether 

 these appearances belonged to the wall or not. If they are internal 

 cells, a series was obtained from the cutting off of one lenticular cell 

 up to five cells. Since the pollen grains of Cycadofilicales and Cor- 



FiG. 66. — Cycadeoidea dacotensis: longitudinal section through strobilus, from a 

 photograph; X2. — After Wieland (22). 



daitales are known to have become multicellular, it would not be 

 surprising to find in the pollen grains of Bennettitales a more exten- 

 sive tissue than is developed in the pollen grains of Cycadales. The 

 formation of swimming sperms cannot be doubted, on account of the 

 structure of the ovule and the relationship of the group. 



