NOTES. 
ON THE SYSTEMATIC POSITION OP ISOETES, L. 
(second note). — In my previous note on this subject (Annals, No. V) 
I discussed some of the principal objections which might be made to 
the inclusion, which I propose, of Isoetes among the Filicinae. But 
there yet remain two important morphological points to be considered, 
namely, the difference in the number and in the position of the 
sporangia on the sporophyll in Isoetes and in the Filicinae respectively. 
Isoetes certainly resembles the Lycopodiaceae, and differs from the 
Filicinae, in that each sporophyll bears a single sporangium on its 
upper (ventral) surface, but this does not appear to be a sufficient 
reason for classifying this plant with the former rather than in the 
latter group. The relation between the Lycopodiaceae and the 
Filicinae in this respect is explained by Brongniart, Mettenius 1 , and 
others, by evidence which tends to show that the single sporangium of 
the Lycopodiaceae corresponds to the fertile ventral segment of the 
leaf of the Ophioglosseae. Now it by no means follows that this 
reduction of a fertile leaf-segment to a single sporangium, or rather to 
what Prantl 2 terms a ‘ monangischer sorus/ did not take place within 
the limits of the Filicinae. On the contrary, if the filicinous characters 
of Isoetes be taken into account, it is impossible to avoid the con- 
clusion that the reduction in question did take place within this 
group. 
In support of this view it may be pointed out that, although there is 
no other case among the Filicinae of such extensive reduction, yet, 
as Prantl 3 has shown, there are many cases of the reduction of the 
sorus to a single sporangium (monangischer sorus), as in Azol/a 
(macrosporangium), Lygodium, Aneimia , Ceratopteris , and the Ophio- 
glosseae. 
1 Mettenius, Ueber Seitenknospen bei Farnen, in Abhandl. d. k. Sachs. Ges. der 
Wiss., V, p. 625, Leipzig, 1861. 
2 Prantl, Bern. ueb. die Verwandtschaftsverhaltnisse der Gefasskryptogamen, &c., 
in Verhandl. d. phys.-med. Ges. in Wurzburg, N. F. IX, 1876. 
3 Prantl, loc. cit ., and Unters. zur Morphologie der Gefasskryptogamen, Heft II, 
Schizaeaceae, 1881. 
