104 
Notes . 
adaxial surface of the frond, rarely upon the margin ; the facts 
accordingly do not support the hypothesis that the many spikes are 
of the nature of pinnae : thus, in Ophioglossum the progression appears 
to be towards multiplication of sporangia and formation of a plurality 
of spikes. 
In Botrychium the progression appears to be from types such as 
B. simplex , in which there is close similarity to a simple Ophioglossum , 
by branching of the spike which is closely connected with enlarge- 
ment and septation of the sporangia, to the condition seen in such 
species as B. virginianum , the branching of the spike running parallel 
with that of the subtending frond. The formation of sporangia 
abnormally on the latter, a condition commonly seen in B. Lunaria , 
but rare in most other species, is believed to be an example of 
reversion of a part typically vegetative to the sporogenous condition, 
and not indicative of a common character of the spike and the vege- 
tative frond. Finally, Helminthostachys occupies an interesting 
intermediate position ; the replacement of the sunken sporangia of 
Ophioglossum by projecting sporangiophores in Hehninthostachys 
suggests, as already indicated in the preliminary statement (Roy. 
Soc. Proc., Vol. 1 , p. 265), an interesting analogy with the hypo- 
thetical origin of the strobilus of Equisetum from a body of the nature 
of a sporogonial head. 
The chief object in view in these investigations has not been the 
mere tracing of homologies of parts among living forms ; but, by 
developmental study and comparison, the following out of the probable 
methods of progression in the evolution of the more complex from 
the simpler types. It is believed that all the three methods of increase 
in number of separate sporangia, suggested in the former memoir 
(Phil. Trans., 1894, Vol. B, p. 473), have been employed, viz. 
(i) septation, (ii) branching or chorisis, (iii) a reversion of vegetative 
parts to the sporogenous condition. In addition to these, however, 
there has probably occurred also an eruption of appendicular organs 
from a previously smooth surface. This has already been suggested 
elsewhere (Annals of Botany, Vol. viii, p. 343) ; the sporangiophores 
of Hehninthostachys may be taken as an interesting example of such 
eruption. It will be thus seen that the memoir, of which this is 
a very brief abstract, touches some of the most fundamental concep- 
tions of the morphology of vascular plants, approaching them, not 
from the point of view derived from comparison of higher forms, 
