REPRODUCTION. 



207 



the cuticularization of the outermost layer of the wall of the em- 

 bryo-sac, it may be said that it is of importance in the processes of 

 nutrition, as is evident from my investigations in regard to the 

 * ' antipodal ' ' cells. It aids in conducting food-materials along 

 definite paths. It has not been demonstrated that such cuticular- 

 ization owes its origin to ' ' phylogeny . ' ' 



I will close this discussion with the following statement : If the 

 great gulf between vascular cryptogams and gymnosperms did not 

 exist, it would not have been necessary for the genius of HOF- 

 MEISTER (in 1851) to introduce a tertium comparationis in the 

 great plant-groups, the vascular cryptogams and gymnosperms. 



It is now necessary to explain some of the special adaptations 

 for reproduction and development among the vascular cryptogams. 



The sporangia of vascular cryptogams usually occur in small 

 groups (sori) upon the lower surface of the leaf, or as shield-like 

 organs on supports, as in Equisetince. Up to the time of maturity 

 these sporangia are usually covered by a protective organ, the 

 indusium, or more rarely by the curled margin of the leaf. The 

 sporangia contain the spores. In the mature sporangia of many 

 ferns (Fig. 128) there is noticeable an incomplete median ring of 



FIG. 128. Aspidium Filix mas. 



A, Vertical section of a sorus &s with indusium t; J?, pinnule with sori; C, single immature 

 sporangium; d, glandular hair. (After Sachs.) 



thickened cells. By a sudden mechanical movement (hygroscopic 

 movement) this ring aids in ejecting the spores. 



