RHIZOCARPEM. 



397 



thick hyaline gelatinous coat which also shows a prismatic structure ((/), but at 

 the same time a concentric stratification. This coat is also not continuous over 

 the apex, but rises above it on all sides forming the outer part of the funnel-shaped 

 entrance to the apex of ihe spore. About this time the dome-shaped bladder-like 



Fig. 297.— Development of the macrospore of /';7K/rtr:a^/<7*j//?/<rrrt ; .v the abortive sister-cells, w the macrospore, 

 A' its nucleus, a the inner, b the outer coat. 



widening of the second coat {U) at the apex appears to burst and to empty itself; 

 in its place is found on the ripe spore (as shown in Fig. 298 //), a conical plicate 

 wart ; the true apical papilla, in which the prothallium is formed on germination, 

 is formed by an arching of the inner coat which now takes place. The prismatic 



Fig. 298.-Further development of the macrospore oi PzMarut slobuli/era ; h cavity of the spore, a the first innercoat, h the 

 second, c the third, d the fourth coat (xSo). 



Structure of the two outer coats of the spore may be considered as an evidence 

 of intersecting lamellar systems perpendicular to the surface of the spores of denser 

 and softer substance ; the third concentric lamellar system is here clearly visible 

 only on the outer coat. The structure of the exospore of Marsilea may also 



