240 MOSSES AND FERNS chap, viii 



the outer cells of the young segment, but is covered by the 

 root-cap, through which the bud afterwards breaks. The sheath 

 covering the first leaf of the bud is formed from the cortex of 

 the root and the root-cap. 



Differing most widely from the other species in general 

 appearance is the curious epiphytic O. {Cheiroglossa) palmatuvi. 

 In this the leaf is dichotomously branched, and instead of a 

 single sporangiophore there are a number arranged in two rows 

 along the sides of the upper part of the petiole and the base of 

 the lamina. 



The genus Botrychiuni includes several exceedingly variable 

 species, the simplest forms, like B. simplex (¥ig. 122, A, B), being 

 very close to Ophioglossuvi, while leading from these is a series 

 ending in much more complicated types, of which B. Virginianum 

 is a good example. In B. simplex the lamina of the leaf is 

 either entirely undivided, as in most species of Ophioglossum^ or 

 once pinnatifid. From this there is a complete series to the 

 ample decompound leaf of B. Virginianum. When the other 

 parts of the plant are studied we find that this greater com- 

 plexity extends to these as well. Thus the sporangiophore is 

 also decompound, and the sporangia entirely free, and showing 

 an approach to that found in such Ferns as Osmunda, and the 

 dichotomous venation of the simpler forms approaches the 

 pinnate type in B. Virginianum. The tissues, especially the 

 vascular bundles, are also more highly differentiated in these 

 species. 



Under favourable conditions well-grown plants of B. Vir- 

 ginianum reach a height of 50 cm. or more, and the sterile 

 lamina of the leaf, which is triangular in outline, may be 

 30 to 40 cm. in breadth, and from three to four times pinnate. 

 The texture of the leaf is membranaceous and not fleshy like 

 that of OpJiioglossum and most species of Botrychium. The 

 sporangiophore is twice or thrice pinnate. The plant sends up 

 a single leaf each year from the underground stem, which is 

 upright and several centimetres in length in old specimens. 

 The roots are thick and fleshy, and much smaller at the point 

 of insertion. As in Ophioglossum each root corresponds prob- 

 ably to a leaf, but the roots branch frequently, so that the root 

 system is much better developed than in Ophioglossum. The 

 secondary roots of B. Virginianum arise laterally, and in much 

 the same way as those of the higher Ferns. As in the terres- 



