XIX] HABIT 49 



of the normally sterile blade may be involved. The importance of this from 

 a theoretical point of view will be discussed later. 



The adult Helininthostachys has a creeping rhizome, usually unbranched, 

 bearing leaves alternately in two rows on its upper surface (Fig. 339), while 

 roots which branch monopodially and are hairless spring from its flanks and 

 undersurface. The stout petiole rising from a flap-like basal stipule bears 

 the large ternate lamina, from the adaxial face of which springs the fertile 

 spike. Borne right and left upon this are serried ranks of sporangiophores 

 covering the margins, and each of them may carry a number of sporangia 

 (Fig. 364, p. 68, F, G: also Fig. 372, p. 73). 



The spike of Helniinthostachys is often subject to accessory branchings, 

 and these may be combined with correlative vegetative growth where 

 sporangia are absent, as in Botrychiuin: the details show that a balance 

 may subsist between the vegetative and the sporangial development 

 (Fig. 344, L-N). Such changes are in line with those seen in other Ophio- 

 glossaceae. 



The genus Ophioglossuin is subject to considerable variety in detail of its 

 numerous species, among which the Common Adder's Tongue, O. vulgatum 

 L., occupies a middle position (Fig. 340). The plant consists of a short 

 upright stock, covered externally by the scars of leaves of previous years: 

 thick, hairless roots, which are commonly unbranched though occasionally 

 showing dichotomy, radiate from it, one being inserted as a rule below the 

 base of each scar; but this arrangement is not rigidly maintained here, and 

 is departed from in other species, as well as in the other two genera. The 

 stem terminates in a bud, and according to season the outermost leaf, or 

 sometimes two of them, may be extended above ground: or the bud may be 

 still enveloped by the ochrea-likestipuleoftheprecedingleaf (j-/^, Fig. 341,1-3). 

 The apex of the axis is buried deep down among the successive leaves, and 

 each of these is provided with a large stipular sheath covering all the 

 younger leaves. There is no circinate vernation. Each leaf develops during 

 three years; expanding in the fourth year it bursts the sheath of the 

 preceding leaf, and forces its way upwards through the soil. The broadly 

 ovate sterile blade finally unfolds as a fleshy expansion with reticulate vena- 

 tion (Fig. 340, D, E). From its upper surface, at the point of junction with 

 the petiole, springs the fertile spike, a stalked body bearing along either 

 margin of its upper part a dense row of sunken sporangia: but the tip of the 

 spike is sterile (Fig. 340, G). Dichotomous branching of the shoot has been 

 described by Poirault and by Petry {Bot. Gas. 191 5, p. 345), but it is rare: 

 the deficiency is made up by the formation of buds which may appear either 

 in relation to the axis as axillary buds (Fig. 341, s), or more frequently 

 upon the roots where they arise close to the apex (Figs. 340, A\ 341, 7). The 

 species is propagated freely by these root-buds. 



Bi II 4 



