1 54 
Double Fertilisation in Angiosperms. 
original nuclei of the sac corresponding to the prothallus, along 
with archegonia, in the Gymnosperms. This idea of a retarded 
prothallus-formation is confirmed by Karsten’s observations on 
species of Gnetum in which a similar phenomenon occurs; but in 
these cases many free nuclei of the endosperm arise before fertili¬ 
sation, while in Angiosperms only two such free nuclei (the polar 
nuclei) are present. In Gnetum Gnemon, where an abundant 
endosperm is developed in the lower part of the embryo sac before 
fertilisation, the later-formed rudimentary endosperm aborts, while 
in the Angiosperms, on the contrary, this is what happens to the 
reduced primary endosperm, while the later-formed endosperm 
persists. In view, therefore, of the fact that the secondary per¬ 
sistent endosperm of Angiosperms is the homologue of the secondary 
aborting endosperm of Gnetum Gnemon, and that there can be no 
possible question of the latter partaking of the nature of an 
embryo, it follows that the former also can never be identified with 
an embryo, and cannot therefore correspond to the second zygote [the 
product of fertilisation ] of Gnetum Gnemon d 
As regards the activities of the second sperm-nucleus, 
Celakovsky points out that if this latter fused merely with the 
sister-nucleus of the ovum, viz., the upper polar-nucleus, the pro¬ 
duct of fusion could hardly be regarded in any other light than as a 
twin-product with the egg. But the idea of a true sexual act in 
connection with the process which actually does occur, viz., fusion 
with the product of union of both polar nuclei, is not to be entirely 
rejected. The first thing to discover is what this “double-nucleus” 
with which the sperm-nucleus has united really is, and especially to 
what cell it belongs. The cell-nucleus of the megaspore or embryo- 
sac, having been resolved into its posterity of eight nuclei, becomes, 
through fusion of the polar-nuclei, regenerated, and its original 
energy restored, this being necessary in order that there might be a 
rapid continuation of the cell-formation which, begun by the primary 
embryo-sac nucleus, had later been interrupted. This secondary 
nucleus also assumes once more the position in the centre of the 
sac which had previously been occupied by the primary nucleus. 
On this hypothesis the endosperm is not a sister-product or twin 
with the embryo, but the retarded portion of the mother-structure: 
the prothallus. Inasmuch as a sperm-nucleus fuses with the polar- 
nuclei it must be assumed that these latter have assumed an actual 
female character, for otherwise the attraction of the male nucleus 
1 See Lotsy's work on Gnetum Gnemon, 
