268 



BOTANY 



'leaves are undivided in most species of Ophioglossum, but in the larger species 

 of Botrychium they are repeatedly divided, not unlike those of the true Ferns. 

 The leaf-bases are developed into sheaths which completely enclose the apex of 

 the stem. The leaves often require three to four years, or even five, for their 

 complete development. 



Sporangium. The sporangia are borne upon peculiarly modified outgrowths 

 of the leaf, the Sporangiophore. This has the form of a spike in Ophioglossum, 

 but may be extensively branched in Botrychium, where the individual sporangia 

 are much more clearly defined than in Ophioglossum. The tetrahedral spores 



FIG. 233. Botrychium Virginianum. A, rhizome and terminal bud of a strong 

 plant, the roots, and all but the base of the oldest leaf cut away (X 1). B, 

 longitudinal section of the terminal bud (X 3). I, II, III, leaves of differ- 

 ent ages; st, stem-apex. C, cross-section of the petiole (X 4). D, cross-section 

 of rhizome (X 16). P, pith; x, wood; ph, phloem; sh, endodermis; m, medul- 

 lary rays. 



are quite destitute of chlorophyll, and are discharged from the sporangia through 

 a transverse cleft. 



Histology of Sporophyte. The ground-tissue is mainly composed of paren- 

 chyma. In the outer cortical region of both stem and root there may be a 

 development of cork. The vascular bundles of the stem are collateral, and in 

 the larger species of Botrychium form a woody cylinder, suggesting the structure 

 of a woody coniferous or dicotyledonous stem. In these a true cambium is 

 developed which causes a regular secondary thickening of the stem. The 

 bundles of the leaves are also collateral in Ophioglossum, but in the large species 

 of Botrychium they approach the concentric type, but never of so perfect a form 

 as in the true Ferns. 



