Ophioglossum (C heir og loss a) palmatum , L. 293 
division, acting as a diffused tapetum. In the Memoir of 1896 1 the results 
of Rostowzew were accepted, without sufficiently critical examination of my 
own preparations, as showing that in Ophioglossum also cells scattered 
through the sporogenous group became disorganized without undergoing 
tetrad division. It has since been found that this is not so, 2 and accordingly 
the comparison with the Psilotaceae on this feature falls away. 
Secondly, the comparison with the Psilotaceae-Sphenophyllaceae alli- 
ance was also based on the method of insertion of the sporangiophore on 
the adaxial face of the leaf. But it now appears that the similarity does 
not extend to the mode of origin of the vascular supply to the fertile 
regions in the plants compared. Dr. Chrysler has laid weight upon the 
marginal attachment of the vascular supply to the spike. The fact is now 
quite plain that, with certain possible exceptions in the specialized O. palma - 
turn , the supply comes off in the Ophioglossaceae either from the margin 
of the petiolar system, or on the abaxial side from an intramarginal gap. 
It may be seen, on the other hand, in any series of sections of the sporophyll 
of Tinesiptevis that the marginal portions of the strand of the leaf-stalk pass 
off right and left into the leaf-lobes, while the central portion enters the 
synangium. The origin of the supply to the sporangiophores in Cheirostrobus 
is described as coming off from the middle strand that supplies the sterile 
region of the leaf, by a branching, so that one of its branches lies above 
and inside the other. 3 That is, the origin is median and adaxial. A simi- 
lar branching appears to be the rule also for Sphenophyllum. These facts 
indicate a real difference between the marginal or slightly abaxial origin of the 
vascular supply to the spike in the Ophioglossales, and the median adaxial 
supply to the sporangiophores in the Sphenophyllales, which if it prove to 
be constant will strengthen the alliance of the former with the Filicales. It 
is of course a possible view, which might be based on the mere anatomical 
facts, that in Tmesipteris the synangium represents the whole terminal 
region of the leaf, which has remained fertile, as in Osmunda regalis . But 
against this are the facts of development ; 4 moreover, that explanation would 
not fit for Sphenophyllum or Cheirostrobus. For these reasons I prefer to 
accept the anatomical distinction as a real and a valid one. 
On the other hand, one of the most impressive features in the Filicales 
is the extraordinary constancy of the progression by which the sporangium 
suffers reduction in size and complexity of structure, in the thickness of its 
gradually elongating stalk, and in the numerical output of its spores as we 
pass from the more primitive to the more specialized forms, while the pre- 
cision of the mechanism for scattering them increases. This matter has 
been treated at length in the ‘ Land Flora 5 (pp. 637-46, &c.). But if the 
1 p. 20. 2 Compare Land Flora, p. 451, Fig. 251. 
3 Scott, Phil. Trans., Series B, vol. clxxxix, p. 12. 
4 Land Flora, p. 414. 
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