I20 



MORPHOLOGY OF GYMNOSPERMS 



spherical, and because the formula does not regard the small spaces 

 between spores, but the error is far less than the variation in the out- 

 put of individual sporangia of 

 average size. It is recognized 

 that this formula could be used 

 only when spores are very small 

 and sporangia very large. Esti- 

 mating in this way, Chamber- 

 lain (63) found the output of 

 spores in Dioon edule to be 

 30,000; Miss F. Grace Smith 

 found it to be 26,000 in En- 

 cephalartos villosus, 8,000 in 

 Ceratozaniia, and 500-600 in 

 Zamia floridana. In general 

 the results favor the view that 

 the output is larger in the more 



Fig. 1 10.- — Dioon edule: microspo- • •■• r i j 



, ., , . , . , , ., primitive forms and decreases 



rangium; detail showing thickened epider- ^ 



mis, wall cells, tapetum, and sporogenous toward the morc highly special- 



tissue; X250. — After Chamberlain (63). ized forms. 



Fig. III. — Dioon edule: microsporangium; two of the sporangia of a sorus, 

 showing extensive sporogenous tissue and scanty tapetum; two-celled hairs growing 

 on the base of the sporangium; X55. — After Chamberlain (63). 



Since the spore is regarded as the first cell of the gametophyte 

 generation, it will be considered in the section on the male gametophyte. 



