148 
Double Fertilisation in Angiosperms. 
His theoretical conclusion with regard to these phenomena is 
that we have before us in these plants a species of polyembvyony , in 
the form of a pair of twin-embryos exhibiting a very dissimilar and 
unequal development, the one remaining thallus-like, in the form of 
the endosperm, and becoming eventually absorbed by the other. His 
view is based on the fact that the normal endosperm arises as the 
result of the fusion of one of the male nuclei with the sister cell of 
the ovum , i.e., with one of the female nuclei; and that therefore we 
have as much right tospeak of this fusion as a sexual act as in the 
case of the actual process of fertilisation itself. At a somewhat later 
date Nawaschin 1 observed “double fertilisation” in certain Dicoty¬ 
ledons. In the case of Helianthus the male nuclei were seen greatly 
to resemble spermatozoids, the polar nuclei were observed to fuse 
before fertilisation of the ovum, and the product of this fusion—the 
embryo-sac-nucleus—after copulation with the second spermatozoid 
was seen to divide rather earlier than was the case with the fertilised 
oosphere. In Rudbeckia similar phenomena occurred. Fusion of the 
polar-nuclei before fertilisation of the ovum was also observed in 
Delphinium datum. It is an interesting fact that Merrel found 
elongated, spirally-twisted bodies (^spermatozoids) in the pollen 
grain of the Composite, Silphium. 
Guignard essentially confirms Nawaschin’s observations. He 
states as a result of his own labours on Lilium Martagon that union 
of both polar nuclei may precede their fusion with the vermiform 
sperm-nucleus and that the latter may subsequently become applied 
to both polar nuclei, but in some cases the sperm-nucleus was 
observed to fuse primarily with the antipodal polar-nucleus; more 
frequently however, copulation with the egg-polar-nucleus is the 
first process, because the latter is the first of the two met with by 
the sperm-nucleus as it passes down the sac. Guignard regards, in 
contradistinction to Nawaschin’s view, the union or fusion of the 
sperm-nucleus with the polar nuclei as a case of pseudo-fertilisation, 
on the following grounds. In true fertilisation both sexual nuclei 
have the same reduced number of chromosomes, whilst the lower 
polar nucleus, as at any rate is known to be the case in Lilium , 
contributes a larger number of chromosomes to the fusion, wi th the 
result that the product of copulation of sperm and polar-nuclei 
possesses a greater number of chromosomes than does the fertilised 
ovum. 
1 “ Ueber die Refruchtungsvorgange bei einigeu Dicotyle- 
doneun” (Berichte der deutsch. Bot.Gesellscliaft, vol. 18, 
1900). 
