1900] SPOROPHYLILS AND SPORANGIA OF ISOETES 335 
Nearly similar evidence is furnished by the male gameto- 
phyte. Though Belajeff (1), to whom we owe the most exact 
investigation of the subject, says the male gametophytes of 
Isoetes and Selaginella afford little ground for relating the two 
genera, he has shown several points of resemblance, such as the 
separation of the prothallial (or rhizoidal) cell from the single 
antheridium by a cellulose wall, and the final dissolution of the 
non-cellulose septa of the antheridium wall, so that the sperma- 
tozoids float free in the cavity of the spore. 
Though not disposed to place much dependence as a clue to 
the working out of phylogenetic relationships among hetero- 
sporous plants on such structures as archegonia and antheridia, 
which must necessarily conform more or less in shape to the 
space in which they are confined, I find some interest in the 
fact that Isoetes and Lycopodium are the only genera of pterido- 
phytes in which the occurrence of more than two neck canal 
nuclei has been reported, and that in Isoetes, as in Lycopodium 
Phlegmaria and Equisetum, the plane of the division of the primary 
neck canal nucleus is at right angles to the archegonium axis. 
The two characters which stand most in opposition to the 
inclusion of Isoetes in the group Lycopodiales are its multicil- 
iate spermatozoid and the embryogeny of its sporophyte. 
Campbell has very properly emphasized the similarity of the 
Isoetes spermatozoids to those of ferns. It requires only a brief 
Survey of the plant kingdom to show the great constancy of the 
form and behavior of male cells in different classes of plants. 
Consider, for example, the non-motile spermatozoids of the Flori- 
deze, or the biciliate spermatozoids of bryophytes. Accord- 
ingly, if we still classify Isoetes among Lycopodiales, we must 
admit that the multiciliate spermatozoids make an exception to 
a constancy which is otherwise remarkable. Unfortunately, we 
have only Lycopodium and Selaginella for comparison, and are 
still in ignorance as to what the gametophytes of the other 
8enera may have to tell us. : 
The embryo of Isoetes finds its nearest approximation in 
Botrychium3 though the resemblance may be only an external 
3Jeffrey (1). 
