VII PTERIDOPHYTA—FILICINEAl—OPHIOGLOSSACE^ 259 



series ending in much more complicated types, of which B. Vir- 

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

 leaf is either entirely undivided, as in most species of Ophioglos- 

 sum, or once pinnatifid. From these there is a complete series 

 to the ample decompound leaf of B. Virginianuin. When the 

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

 plexity extends to them as well. Thus the sporangiophore is 

 also decompound, and the sporangia entirely free, showing an 

 approach to those of such Ferns as Osmiuida; and the venation, 

 which in the simpler forms is dichotomous, approaches the 

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

 vascular bundles, are also more highly differentiated in the 

 larger species. 



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

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

 lamina of the leaf, wdiich 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 Ophioglossiun and most species of Botrychiuin. The sporan- 

 giophore 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 Ophioglossmn each root corresponds probably to a leaf, but 

 the roots branch frequently, so that the root system is much 

 better developed than in Ophioglossiun. The secondary roots 

 of B. Virginianum arise laterally, and in much the same way as 

 those of the higher Ferns. As in the terrestrial species of 

 OpJiioglossuiu, the development of the leaves is very slow. 



In most species of Botrychiuin the relation of the leaf base 

 to the young bud and stem apex is the same as in Ophioglossuni, 

 except that the sheath is more obviously formed from the leaf 

 base ; but in B. Virginiannni the sheath is open on one side, and 

 more resembles a pair of stipules. Fig. 142, A shows the stem 

 and terminal bud of a plant of this species with all but the base 

 of the leaf of the present year cut away, and B the same with the 

 bud cut open longitudinally. At this stage the parts of the 

 leaf for the next year are well advanced, and the formation of 

 the individual sporangia just begun. The leaf for the second 

 year already shows the sporangiophore clearly evident, and the 

 leaf which is to unfold in three years is evident, but the sporan- 



