XI 



LEPTOSPORANGIATJE HETEROSPOREJE 



415 



pletely closed. In the former, before this happens, filaments of 

 Anabcena creep in and enter the resting condition. Thus they 

 remain until growth is resumed with the germination of the 

 spore, when the embryo is infected. The upper cells of the 

 indusium become very dark-coloured and hard, and remain after 

 the lower part decays. The wall of the macrosporangium does 



A. 



B. 



FIG. 241. A, Young microsporangial sorus of A. filiculoides, X8o; col, columella; id, 

 indusium; B, nearly ripe microsporangium, X225- 



not become absorbed, as Strasburger ((6), p. 71) states, but 

 remains intact, though very much compressed, until the spore 

 is ripe. 



The sporocarps of Salvinia are like those of Azolla, but the 

 two layers of cells are separated by a series of longitudinal air- 

 spaces which correspond to ridges upon the surface of the sporo- 

 carp (Fig. 233, D). 



The microsporangia of Azolla have a long stalk, which is 

 composed of usually two, but sometimes three rows of cells. 

 The sixteen sporogenous cells all develop, so that there are 

 normally sixty-four microspores in each sporangium. These 

 have the exospore thin and smooth, and are included in a kind 

 of common epispore, which here too owes its origin mainly to 

 the tapetal cells. This episporic substance is divided into 

 masses (massulae), which have the foamy structure of the 

 episporic apendages of the macrospore. This appearance is 

 apparently clue to the formation of vacuoles, which make these 



