453 STUDIES IN FOSSIL BOTANY 



entering the seed. The multicellular structure of the 

 pollen-grains, in this and other cases, was first demon- 

 strated by Renault, and fully confirmed by the more 

 recent observations of Oliver, who finds that there are 

 about twenty cells in each grain, so arranged that five 

 radial septa are seen when the grain is cut transversely 



Fig. 173- — Stcphanospcrmuiit a-kenioides. Upper part of pollen-chamber, showing part of 

 its wall, with the base of the beak. In the chamber a large multicellular pollen- 

 grain is shown, also three small foreign pollen-grains, one of which partly overlies 

 the large grain. X 90. Will. Coll. 1486a. From a photograph leat by Prof. 

 F. W. Oliver, F.R.S. 



(Fig. 174). Ultimately the internal cells appear to have 

 become retracted towards the periphery, leaving behind 

 them in the middle of the grain a framework of cell- 

 wall — the " replum " (see Fig. 174). 



In the light of our present knowledge of the repro- 

 duction of Ginkgo and the Cycads it is an obvious 

 suggestion that the internal cells of the pollen- 

 grain were antheridial cells, producing spermatozoids. 



