Notes on Recent Literature. 
378 
a prothallus whose development before fertilisation has stopped at 
that stage, the further development of the prothallus so formed being 
the result of a nuclear fusion which acts as a stimulus to renewed 
division. This view was generally held until the discovery that 
a male nucleus entered into the fusion, when it became necessary to 
explain the phylogenetic origin of the so-called “ double fertilisation.” 
Various suggestions' were made, of which the one most favoured 
was that of Sargant—that the union of the upper polar nucleus 
(sister of the egg) and the male nucleus may be a true fertilisation, 
but that the introduction of the lower polar nucleus causes the trans¬ 
formation of the embryo which should have arisen from this union 
into a monstrous short-lived tissue, serving for the nourishment of 
the embryo. 
Strasburger’s hypothesis regarded the antipodals as merely 
prothallial cells which have lost their original function and are now 
of an evanescent nature, except when they have taken on a new 
function, that of absorbing food from the nucellus. Many later 
writers, however, have considered that the polarity of the antipodal 
group, as compared with the egg-apparatus, and the behaviour of 
these cells when they do function, suggest that they represent the 
vegetative tissues of the gametophyte. This view has gained its 
chief support from Lotsy’s investigations on the embryo-sac of 
Gnetum gnemon , 2 which he described as containing a sterile prothallus 
in the lower part, and free fertile nuclei in the upper. 3 The 
Angiosperm embryo-sac has been compared with this, the anti¬ 
podals and lower polar nucleus being considered as equivalent to the 
sterile vegetative portion, and the egg apparatus and upper polar 
nucleus to the fertile nuclei. 
Lotsy himself, however, deduced other homologies from Gnetum 
gnemon. He regarded the antipodal cells as equivalent to a 
degenerate egg-apparatus, and the two egg-apparatus thus present 
in the sac as representing the remains of the archegonia—the rest 
of the prothallial tissue being reduced to the two polar nuclei. 
Somewhat similar homologies have lately been elaborated by 
Porsch, 4 who considers that in the Angiosperm we have a prothallus 
so reduced as to consist solely of two archegonia, represented by 
the egg-apparatus and the antipodals respectively. He even 
homologises the cells composing these two groups with the 
components of an archegonium—thus the synergids represent the 
neck-cells, and the two polar nuclei are the ventral canal cells of 
the two archegonia; and as the ventral canal cell is the sister of 
the egg, he regards triple fusion as a kind of fertilisation and the 
endosperm as a modified embryo. In considering this theory, it 
must be remembered that the archegonium in Gymnosperms appears 
at a much later stage in the life-cycle, and that it is necessary to 
explain how such a specialised structure could be represented 
in so reduced a gametophyte as that of the Angiosperms. 
Moreover, the archegonium itself has disappeared in the highest 
group of the Gymnosperms, so that in Welwitschia and Gnetum 
1 Sargant, 1900; Land, 11)07 ; Thomas, 1907; Berridge, 1907. 
2 Lotsy, 1899. 
3 Coulter, 1908 (b), however, describes the embryo-sac in this 
species as containing only free nuclei, Lotsy’s sterile prothallus 
being, according to him, merely deeply staining “pavement 
tissue ” of the nucellus at the base of the sac. 
4 Porsch, 1907, pp. 19, 20. 
