254 



THIRD GROUP. VASCULAR CRYPTOGAMS. 



with Angiopteris. Each sporangium in Marattia and in Angiopteris opens by a 

 longitudinal fissure on its inner side. In Kaulfussia the eight to twenty sporangia in 

 a sorus are arranged in a circle, and have grown together so as to form a plurilocular 

 structure ; they, too, open by a longitudinal slit on the inner side. In Danaea the 

 united sporangia are in two long rows which cover the entire length of the vein that 

 bears them, and each compartment or sporangium opens by a hole at its apex. 

 Round the sorus are usually some flat lobed hairs forming a kind of indusium, which 

 in Danaea looks like a cup in which the long sorus lies. 



The history of the development of the sporangia is in essential points the 

 same in Angiopteris and Marattia. The placenta is a cushion-like protuberance 

 from epidermal cells above a vascular bundle. In Angiopteris two rows of papillae 

 appear separate from one another on the placenta, each of which proceeds from 

 a group of cells on the surface of the placenta. Each papilla developes into one 

 of the free sporangia of the sorus. The hypodermal terminal cell of the central 



FIG. 207. A under side of the upper portion of a leaflet of Angiopteris caiidata with the sori s s. B teeth of the margin 

 of a leaf of Marattia with the sori ss. C half of a sorus of Marattia. with open sporangia (compartments). 



row of cells (Fig. 208, where it is divided already by a longitudinal wall) is the 

 archesporium ; the tapetal cells come from the surrounding tissue. Each of the 

 sporangia which are united together laterally in Marattia has its own archesporium, 

 which originates exactly as in Angiopteris ; this proves that in Marattia, as in 

 Angiopteris, we have two rows of distinct sporangia which have grown together by 

 their lateral faces. 



The spores are formed from their mother- cells in the usual manner; bilateral 

 bean-shaped spores and spheroid-tetrahedral spores occur in the same species, but 

 there is no difference in their mode of germination. 



The wall of the mature sporangium is formed of several layers of cells ; the cells 

 of the outermost layer have thick dark-coloured walls, especially at the apex of 

 the sporangium ; this structural arrangement recalls the rudimentary annulus of the 

 sporangium of Osmunda. The cells in the parietal layers have thinner walls in the 

 place where the sporangium dehisces than elsewhere, as is the case also in Botrychium 



