2 53 
Life- History of Isoetes . 
and In having numerous cilia. All lycopods yet examined 
have bi-ciliate spermatozoids like those of the bryophytes. 
The embryo, too, in the absence of a suspensor common to 
many, at any rate, of the Lycopodineae, as well as to the 
arrangement of its members, points to a genetic connection 
with the ferns rather than the lycopods. Unfortunately we 
have no account of the young embryo of any of the eusporan- 
giate ferns, with which Isoetes ought to have a closer connection 
than with the leptosporangiate forms. 
Taking into consideration, then, the data at our disposal, 
the weight of evidence seems to be in favour of regarding 
Isoetes as belonging rather to the Filicineae than to the 
Lycopodineae. 
As to the affinities of Isoetes with the spermaphytes, in 
regard to the formation of the female prothallium, it more 
nearly resembles them than it does any pteridophyte with 
the possible exception of Selaginella\ and in the absence 
of any distinction between the prothallium proper and endo- 
sperm, is certainly nearer the spermaphytes than is the 
former. The reduction, too, of the antheridium, producing 
but four spermatozoids, is greater than in any other pterido- 
phyte. 
The embryo, in the absence of a suspensor, differs very 
widely from that of the gymnosperms, even the cycads with 
which Bower 1 suggests there may be a relationship, and 
among the spermaphytes the monocotyledons offer the near- 
est approach to it in structure. The lateral formation of the 
stem-apex, as for instance in Alisma (see Goebel, ‘ Outlines/ 
Fig. 332), is extraordinarily similar to its formation in Isoetes , 
as well as the relative positions of the single cotyledon and 
root ; and this together with the histology of the grown sporo- 
phyte, the leaves with their sheathing bases surrounding the 
short, bulb-like stem, and the structure of the roots, all 
suggest a possible relationship to the monocotyledons directly 
rather than with the gymnosperms. Certainly the develop- 
ment of the prothallium would hardly be an argument against 
1 Annals of Botany, vol. III. No. XI. p. 387. 
