FTL TCI NEAR. — OPHIO GL OSSEA E. 



249 



the sporangiferous branch proceeds from the middle of the leaf-stalk, as in Botrychium 

 rutaefolium and dis sec turn. 



The structure of the sporangia in the Ophioglosseae agrees in the main with 

 that of the same organs in the Marattiaceae. The sporangium in Botrychium is a 

 roundish capsule opening by a transverse fissure; the spot in the wall where this 

 fissure afterwards appears is recognisable at an early stage by the presence of smaller 

 cells with more delicate walls. The wall of the sporangium is formed of several 

 layers of cells, the outermost of which passes below into the epidermis of the 

 sporophyll. The young sporangia of Botrychium Ltmaria are clusters of cells, 

 forming hemispherical protuberances ; they take the place of pinnules of the fertile 

 portion of the leaf (sporophyll), but appear subsequently to have been moved to its 

 upper (inner) side. The terminal cell of the axile row beneath the epidermis is the 

 archesporium, which acts as mother-cell of the sporogenous tissue (see Fig. 208). 

 The sporogenous cells are here, as in all sporangia, surrounded by layers of tabular 

 cells, the tapetal cells, which are not employed to form the spores, but are eventually 

 disorganised. 



In Ophioglossum the mature sporangia form curved cavities in the tissue of the 

 fertile portion of the leaf and on its lateral faces, but somewhat nearer to one margin. 

 A longitudinal section through the immature sporangiferous branch of O. vulgatum 

 (Fig. 204) shows that the outer layer of the wall of the sporangia is continuous with 

 the epidermis of the entire fertile branch of the leaf, and is furnished with stomata ^ ; 

 at the spots where the lateral transverse fissure appears in each sporangium these 

 epidermal cells are radially elongated, and the whole layer lies in an indentation 

 which is at first scarcely perceptible. The spherical cavities which contain the mass 

 of spores are deep in the tissue of the organ and are entirely surrounded by its 

 parenchyma ; some layers of this parenchyma are also present on the outer side 

 where the transverse fissure afterwards arises ; the middle part of the parenchyma is 

 traversed by vascular bundles which anastomose and form long meshes, and send off" 

 a bundle in a transverse direction between every two sporangial cavities. 



A similar arrangement will be found in Botrychium, if we compare the separate 

 lobes of the sporangiferous branches with the sporangiferous branch in the Ophio- 

 glosseae ; the sporangia in both cases are in two rows and alternate, but in Botrychiwii 

 they are rounder and more prominent because the tissue of the branch is less 

 developed between each pair of sporangia. Each mother-cell produces four spores, 

 dividing, after indication of bipartition, into four segments tetrahedrally disposed and 

 surrounded each by a delicate membrane, the special mother-cells ; the protoplasm in 

 each of them becomes invested with a new and firmer cell-wall, the true coat of the 

 spore, and then the walls of the segments are dissolved and the spores are set at liberty. 

 In specimens preserved in spirit the young spores of both genera still hanging together 

 in fours are seen imbedded in a colourless, granular, coagulated jelly, which evidently 

 is the same as the fluid in which the. spores of the rest of the Vascular Cryptogams 

 float in the living plant before they are mature. The spores are tetrahedral, and in 

 Botrychium are furnished when still young with knob-like prominences on the 

 cuticularised exosporium. 



' This is not the case in the early condition of the sporangia. On the history of their develop- 

 ment see Bot. Ztg. 1881. 



