6o 
Farmer . — On Isoetes lacustris , Z. 
sperm. It may be that the one nucleus contains sufficient 
histogenic plasma (to borrow Weismann’s expression) to 
enable, under suitable circumstances, the ‘reproductive sub- 
stance’ provided by the other nucleus (the sister-nucleus of 
the oosphere) to go through that simple form of segmentation 
which characterises the endosperm of Angiosperms. 
This view of the matter makes the micropylar nucleus, be- 
fore it divides into the four nuclei which compose the original 
‘ egg-apparatus,’ the equivalent of the ‘ central cell’ of a Fern- 
archegonium; it cuts off successively two polar bodies, of which 
the first gives rise to the synergidae by further division, just 
as the neck-canal-cell of Ferns commonly divides further, after 
its separation from the central cell ; and the second one, which 
I regard as representing the ventral canal-cell of the Fern, forms 
half the definitive nucleus. It is true the existence of a ventral 
canal cell has been denied in the case of some plants, but 
the point requires renewed investigation. And there is nothing 
surprising in such a reduction of the generative apparatus in 
the highest plants ; such a process is indicated all through the 
various lines of descent of the different branches of Vascular 
Cryptogams, as well as of the Gymnosperms. In the Angio- 
sperms indeed, bearing in mind how the tissue for the support 
of the growing embryo is not even capable of developing 
unless there is a chance of its being used, and also how 
this principle of saving material is carried yet further in the 
case of ovules of many Orchids, such a reduction as actually 
occurs in the embryo-sac is not only possible but inherently 
probable. 
If these conclusions be accepted, Isoetes becomes additionally 
interesting as throwing light on some of the most obscure 
phenomena prevailing in Angiosperms. Its connection with 
Selaginella is equally interesting, as serving to explain the 
peculiarities of the sexual generation of this plant, but I do 
not regard the approximation in the character of the two 
oophytes as affording any weighty arguments for placing them 
near each other in the natural system. Rather we have an 
indication of one of those ‘parallel developments/ which are 
