FILICINEM. 



419- 



if the history of its development alone decided the question, and then it would 

 offer no analogy to the same structure in Angiopteris. But analogy clearly indicates 

 that in Alarattia we have not to do with a multicellular sporangium but with a 

 sorus, the individual sporangia of which have become united. Like those of 

 Angiopteris^ each of these sporangia opens by a longitudinal slit upon its inner 

 surface. It is of but little importance for this interpretation that the apparently 

 multicellular sporangium, which we regard as a coalesced sorus, is borne in 

 Eiipodium {Mar. Kaulfussii) on a stalk of considerable height, for the sorus in 

 many of the true Ferns {Cyathea, Thyrsopteris) is also stalked. It can scarcely 

 be doubted therefore that the multicellular fructification of Marattia is a coalesced 

 sorus, and the same holds good also for Kaulfussia and Daticea. In Kaulfussia 

 the sporangia of a sorus (from eight to twenty in number) are arranged in a circle 

 and are united to form a many-chambered ring. Each opens on its inner side 

 by a longitudinal slit. This arrangement is even more striking in Dancea, where 

 the united sporangia form two long rows covering the vein bearing them throughout 

 its whole length, and where each chamber (sporangium) opens at its apex. The 

 sorus is usually surrounded by flattened lobed hairs forming a kind of indusium, 

 which, in DancBa, appears like a kind of cup in which the sorus lies. Luerssen's 

 argument that these outgrowths of the epidermis are not to be regarded as an 

 indusium because they occur elsewhere upon the leaves and are therefore merely 

 hairs, is not valid, for the indusium of the true Ferns is a hair-like outgrowth, and 

 must be regarded as a trichome. As in the Ferns, so in the Marattiaceae, the 

 indusium does not occur in all species. 



The development of the sori has been studied by Luerssen and by Goebel 

 in Marattia, and by these observers and by Tschistiakoff in Angiopteris. In both 

 cases the placenta arises as a cushion-like protuberance from the fertile vein of 

 the epidermis and the subjacent tissue. In Angiopteris two separate rows of 

 papillae make their appearance upon the receptacle, each of which consists from 

 the first of a group of cells derived from a group of the superficial cells of the 

 placenta. Each papilla becomes one of the free sporangia of the sorus. In 

 very young sporangia Tschistiakoff was able to detect an internal cell (arche- 

 sporium) surrounded by two or three layers of cells which gave rise by repeated 

 division to a group of spore-mother-cells. In Marattia two parallel swellings 

 appear on the placenta, which soon become separated by a deep and narrow fold. 

 In each of these swellings a row of cell-groups, the mother-cells of the spores, 

 are differentiated, which have been formed by the division of the archesporium. 

 Each of these groups corresponds to a sporangium, the walls of adjacent sporangia 

 coalescing from the first. The inner surfaces of the two parallel swellings approach 

 each other more and more closely as development proceeds, but they separate 

 widely when the spores are ripe, so that the multilocular fructification splits longi- 

 tudinally into two halves, and the loculi of each half open by vertical slits upon 

 their inner surfaces. 



The development of the spores, four from each mother-cell, differs but little 

 from that of the Ophioglossese and the Ferns. It is important to note that in 

 the Marattiaceae the wall of the mature sporangium consists of several layers of 

 cells, whereas in the Ferns it consists only of one. 



