66 OPHIOGLOSSACEAE [ch. 



the spike as a result of coalescence of two basal pinnae (Fig. 359). In B. vir- 

 giniajium, however, in which the pinna-traces are extra-marginal, the supply- 

 to the fertile spike arises in a similar way to these (Fig. 360, compare A , B), by 

 separation of an extra-marginal part of each of the two meristeles, and these 

 together supply the spike (Chrysler, Ann. of Bot. 1910, p. i). In the fertile 

 leaf of Helminthostachys the ring of small petiolar strands segregates with 

 very complicated fusions and splittings into four groups, each of circular 

 outline (Fig. 361). The adaxial group which is the weakest, passes upwards 

 into the spike {sp\ the other three which resemble it, though stronger, supply 

 the sterile segments. These anatomical facts support the pinna-origin of 

 the fertile spike. Some of the spikes of O. palmatuvi it is true arise super- 

 ficially, and appear to have an intra-marginal vascular supply: but in others 

 it has been seen to be truly marginal (Fig. 362). 



Structure and Development oe the Fertile Spike 



It is a significant fact that all the fertile spikes of the Ophioglossaceae 

 bear their sporangia in a marginal position, though there is some difference 

 of detail in their exact relations. The simplest arrangement is that in 

 OpJiioglossum, where the large sunken sporangia are fused laterally so as to 

 form a dense series right and left of the midrib, but stopping short, as a rule, 

 of the apex of the spike (Fig. 364, A, B). When mature each opens by a 

 transverse slit, the dehiscence being determined by two rows of cells smaller 

 and less indurated than the rest of the wall. Small branchlets from the 

 vascular supply of the midrib pass outwards into the septa between the 

 sporangia. The spore-output of each is very large: in O. pendulum it has 

 been estimated roughly at 15,000. The disposition of the sporangia on the 

 usually branched spike of Botrychiuvi is according to the same plan, but 

 with the sporangia isolated, though occasionally they may be fused synan- 

 gially (Fig. 364, C, D, E). They also open by a transverse slit: the spore- 

 output is here lower, and may be estimated at 1500 to 2000 from each. In 

 Helminthostachys the spike is more complex, the sporangia being borne on 

 outgrowths of the nature of sporangiophores, which are disposed in serried 

 ranks right and left along lines clearly corresponding to the lines of sporangia 

 in Ophioglossum and BotrycJiium (Fig. 364, F\ Each sporangiophore has its 

 own vascular supply, and bears a varying but small number of sporangia 

 irregularly disposed, while its apex ends in irregular vegetative lobes. The 

 sporangia are approximately of the same size as in Botrychium, and they 

 open by longitudinal slits (Fig. 364, G). It is clear that the spikes and 

 sporangia are comparable in all the three genera, and may be held as 

 variants of the same organs. 



The development of the fertile spike has been traced in Ophioglossum from its first 

 beginnings. The leaf itself originates very close to the initial cell of the deeply depressed 



