414 



VASCULAR CRYPTOGAMS. 



the middle of the lamina {0. pcnduluni), or the two branches of the leaf appear as if 

 separated deep down to their origin {0. Bergianum)^ or, finally, the fertile branch 

 springs from the middle of the leaf-stalk {Botrychium rutafolium and dissecium). 



The Sporangia of the Ophioglossaceae are so essentially different from those of 

 Ferns and Rhizocarps that these plants cannot, for this reason, be arranged in 

 either of these classes. They arise from several epidermal cells. The wall of the 

 sporangium consists of several layers of cells, its outer limit being formed by the 

 epidermis of the leaf itself. The mother-cells of the spores in Botrychium Lunaria 

 and probably also in Ophioglossum are derived, according 

 to Goebel {loc. cii), from a single central cell (archesporium) 

 which is invested by peculiar cells (forming the tapetum) 

 developed by the division of the surrounding cells of the 

 sporangium. A longitudinal section through the unripe 

 so-called spike of O. vulgatum (Fig. 290) shows that the 

 outer layer of the wall of the sporangium is a continuous 

 prolongation of the epidermis provided with stomata and 

 covering the whole of the fertile branch of the leaf. At 

 the places where the lateral transverse line of dehiscence 

 subsequently appears in each sporangium, these epidermal 

 cells are elongated radially, and the whole layer exhibits 

 an indentation at first scarcely perceptible. The spherical 

 cavities which contain the masses of spores are imbedded 

 in the tissue of the organ, and are therefore entirely sur- 

 rounded by its parenchyma, there being several layers of 

 it on the outer side where the transverse fissure subsequently 

 arises. The middle part of the mesophyll is penetrated by 

 fibro-vascular bundles which anastomose with one another 

 into long meshes, and send out a bundle transversely between 

 each pair of sporangial cavities. The course of development 

 is the same in Bot7ychium, if the separate sporangiferous 

 branches of the panicle are compared with the spike of 

 Ophioglossum. The sporangia are similarly placed on them 

 in two rows and alternate ; only they project further because 

 the tissue between each pair of sporangia is but slightly 

 developed. Four spores are formed from each mother-cell. 

 The mother-cell, after an indication of a division into two, 

 divides into four segments, each surrounded by a delicate 

 cell-wall. The protoplasm of each of these special mother- 

 cells becomes invested by a new wail, the true wall of the spore, and the primary 

 walls become absorbed, so that the spores become free. In specimens of both 

 genera preserved in spirit, the young spores, still connected together in fours, are 

 found imbedded in a colourless, granular, coagulated mass of jelly, which in the 

 living plant clearly corresponds to the fluid in which the spores of other Vascular 

 Cryptogams float before they are ripe. The spores are tetrahedral ; in Botry- 

 chium they are provided, even in a very early state, with knob-like projections on 

 the cuticularised exospore. 



Fig. 290.— Longitudinal section 

 through the upper part of a spike 

 of Ophioglossum vulgatum ; s 

 its free apex, sp the sporangial 

 cavities, r the part where they 

 burst transversely; g the fibro- 

 vascular bundles (X about lo). 



