OPHIOGLOSSACEJ: 



99 



soil at the commencement of the fifth year ; where there are several 

 leaves, the points of origin of those of successive years have a spiral 

 phyllotaxis. They are quite simple and entire, simply pinnate, or twice 

 or thrice pinnate. There is always a long petiole, which is furnished 

 with a ligular or sheath-like outgrowth on each side ; and the coalescence 

 of these appendages forms a hollow chamber within which the leaf is 

 developed, similarly to what takes place in Marattiaceae. They are 

 never circinate in vernation. They are of coriaceous texture, and are 

 always quite glabrous, and possess a well-defined epiderm furnished 

 with stomates on both surfaces, and in immediate contact with the 

 mesophyll, without any intermediate hypodermal layers. The mesophyll 

 is large-celled and spongy, with large intercellular 

 spaces. The 'vascular' bundles are but feebly deve- 

 loped ; they anastomose in Ophioglossum, but only 

 dichotomise in Botrychium and Helminthostachys. 

 In most species all the leaves are fertile ; but in Rhi- 



FlG. 



76. Ophioglos- 

 sum vulgatum. Por- 

 tion of sporophyll 

 with closed spo- 

 ranges, s ; g; ' vas- 

 cular ' bundle ( x 10). 



FIG. 75. Botrychium Lunarict. Portion of sporophyll with 

 open sporanges (magnified). (After Luerssen.) 



zoglossum (Presl) (a section of Ophioglossum) there 

 are both barren and fertile leaves. The leaf divides 

 at an early period into two branches an outer branch 

 which is sterile, and which alone develops chlorophyl- 

 lous parenchyma; and an inner fertile branch, the sporo- 

 phyll, which springs either from the base or middle of 

 the lamina or from the leaf-stalk. This branch never 

 has any green parenchyme except in Helmintho- 

 stachys. 



The sporanges resemble in their origin and mode of formation those 

 of Marattiaceae. They are not formed from a single cell, but from a 

 group of cells in the substance of the sporophyll which are differentiated 

 from the surrounding tissue. The terminal cell of the axial row beneath 

 the epiderm is the archespore from which all the spores are formed ; it 

 is surrounded by the layers of mantle-cells constituting the tapete, 

 which are formed out of the epidermal cell immediately above the 

 archespore, and which ultimately disappear. The wall of the sporange, 

 consisting of several layers of cells, is developed from the epiderm, and 

 contains stomates. Strasburger regards each sporange as corresponding 

 homologically to an entire sorus in the Filices being, in fact, a meta- 



H 2 



