54 OPHIOGLOSSACEAE [ch. 



The formation of axillary buds has been proved in all the three genera. 

 They were first seen by Gwynne-Vaughan in Helminthostachys, as minute 

 groups of embryonic cells seated each at the base of a narrow axillary canal 

 above an interruption of the endodermal cylinder (Fig. 346). There is one 

 present in each leaf-axil. Commonly they are dormant, but may be stimulated 

 into activity by injury of the main shoot. Similar axillary buds have been 

 described by Bruchmann and by Lang as practically constant in Botrychiinn 

 Lunaria, and they occasionally develop into actual branches. The facts for 

 Ophioglossuni have been less clearly made out, but in presence of the drawings 

 of Rostowzew we cannot deny the existence of lateral branching, apparently 

 of axillary origin, in that genus also (Fig. 341, 8). Such facts supply a basis 

 for comparison not only with the living Hymenophyllaceae, but also with 

 the ancient Zygopterideae, in both of which axillary buds are known to exist 

 (Lang, Studies, iii, p. 47). 



Meristems 



In the structure of their apical meristems the Ophioglossaceae occupy a 

 middle position, since they possess a single initial in some of their parts, but 

 its form and segmentation are not constant, and sometimes the identity 

 of the initial is obscure. The root in all three genera has an initial cell of 

 tetrahedral form, and a segmentation of the usual type, though less regular 

 than in Leptosporangiate Ferns," The apex of the stem is deeply sunk, and 

 a single initial is present, but it may be either a three- or a four-sided prism 

 with a truncate base {O. vulgatwii), or more commonly it is pointed below, 

 and is certainly so in Botrychimn (Campbell, Mosses and Ferns, p. 262), 

 There is some difficulty in tracing the origin of the young leaves: but it 

 seems probable that one of them corresponds to each segment of the initial 

 cell, as in some Leptosporangiate Ferns. At first the young leaf also shows 

 a single initial, but subsequent growth is largely intercalary, and there is no 

 accurate segmentation comparable with that seen in the leaf-apex of most 

 Ferns. This fact goes along with the absence of circinate vernation. The 

 sporangia of the whole family are eusporangiate; and though the sporo- 

 genous tissue, together with part of its covering wall, is referable as a rule 

 to a single initial with regular segmentation, the sporangium as a whole 

 originates by outgrowth of a number of constituent cells, as it does in the 

 Marattiaceae (Figs. 370, 371). 



The detailed study of segmentation has lost in late years much of its 

 glamour. We are still ignorant of the causes influencing it, and it will not 

 resume its lost position till a better knowledge it attained. But it still keeps 

 its comparative value, however little its causes may be understood. The 

 general thesis has been developed in Vol. I, Chapter VI, that there has been a 



