Notes. 
I 2 I 
and in Selaginella, but there is the well-known difference in the 
germination of the macrospores. 
These differences between Isoetes and the recognised members 
of the Lycopodinae are surely sufficiently striking to raise a doubt 
as to the propriety of continuing to include them all in one group, 
and thus the question is raised as to what other position can, with 
any probability, be assigned to Isoetes. 
In its general habit, and in the absence of sporangiferous cones 
and specially differentiated sporophylls, Isoetes resembles the Filices, 
as also in the more general features of its embryogeny. This re- 
lationship is emphasised in a remarkable manner if, as Sadebeck 
suggests 1 , the velum of Isoetes be truly homologous with the 
indusium present in many Filices and in the Salviniaceae. It must 
be admitted, however, that both the male and female gametophytes 
of Isoetes resemble rather those of Selaginella than those of the 
Hydropterideae. 
The general tendency of these remarks would seem to be towards 
a reunion of Isoetes with the Rhizocarpae ; but in view of Goebel's 
researches on the development of its sporangium this cannot be done. 
Isoetes is distinctly eusporangiate, whereas the Rhizocarpae are as 
distinctly leptosporangiate. If Isoetes is to be included in the 
Filicinae, it must be connected with the eusporangiate forms of that 
group. This is, in fact, the answer to the question as to the 
systematic position of Isoetes , if removed from the Lycopodinae : 
it is a heterosporous form, the only one hitherto recognised as such, 
of the Eusporangiate Filicinae. It certainly resembles the Ophio- 
glosseae and the Marattiaceae in its general habit; in Isoetes as 
also in these forms the stem is remarkable for its extremely small 
longitudinal growth, for the consequent absence of internodes and 
of branching, for the entire concealment of its surface by the 
insertions of the leaves, and for the formation of roots in acropetal 
succession close behind its apex. There is a more special point 
of resemblance, though it may amount to no more than an analogy, 
between the imperfectly multilocular sporangia of Isoetes and the 
compound sporangium of most of the Marattiaceae. 
Doubtless, many objections will be raised to this view of the 
1 Sadebeck, Die Gefasskryptogamen, in Schenk’s Handbuch der Botanik, I 
p. 326 k, 1879. 
