HETEROSPORY 



333 



retained within the original spore wall. In these ferns 

 the other kind of sporangium produces a few — some- 

 times only four — large spores. They are eight to ten 



Fig. 87. — Selaginella. A, a branch showing the leaves arranged 

 in four rows and the branches tipped with cones or strobiH. B, a 

 sporangium-bearing leaf from the cone with a microsporangium 

 filled with the small sort of spore or microspores. C, a sporophyll 

 or sporangium-bearing leaf with a megasporangium containing four 

 large or megaspores. D, and E, showing comparative size of micro- 

 spores and megaspores. The latter are from 8 to 10 times the 

 diameter of the former and consequently from 500 to 1000 times as 

 large in contents. 



Coulter, Plant Structures. Appleton. 



