1 53 
Double Fertiliser!ion in Angiosperms. 
distinct stages, 1 the first stage consists in the formation of the 
synergids and antipodal cells } after the third division, resulting in 
the production of the eight nuclei in the sac, these latter no longer 
possess the power of dividing further ; hence an interruption in the 
process of prothallus-formation, during which interval fertilisation 
of the ovum takes place. But it can be readily seen that, should 
this latter function fail to he performed, the formation of endosperm 
(prothallus) would entail a great waste of energy, hence we find 
that in the vast majority of cases the latter is made dependent on the 
former. But, and here we reach the core of the whole problem, 
inauguration of the second stage of prothallus-formation must be 
effected by some fresh stimulus', and this is afforded by the second 
sperm-nucleus, which, through fusion with the definitive nucleus of 
the sac, increases the nuclear substance of the latter, inducing 
thereby the divisions which constitute the second stage of prothallus- 
or endosperm-formation to proceed rapidly. The interesting results 
obtained in Maize-cultures, which led Correns to entertain the 
mistaken idea that this “double fertilisation” constituted a process 
of true fertilization, could hardly have been different when fusion 
between the sperm and the definitive nucleus takes place. 
The whole character of the endosperm is antagonistic to the 
idea of its being a second “nutritive embryo.” Yet he suggests 
that the process which now consists merely in a stimulus may in 
the course of time have been degraded from a process of true 
fertilisation. 
Strasburger cites cases where, in the absence of fertilisation, 
the formation of endosperm may take place, e.g., in Ccelebogyne 
(where adventitious embryos occur), Ranunculus midtifidus, Anten- 
naria alpina (in which each polar-nucleus divides independently), 
and Balanophora elongata (in which the upper polar-nucleus only 
divides). He mentions that these cases may possibly represent 
reversions to the time when the sac became filled with a prothallus 
before fertilisation. 
Celakovsky, 2 the great Bohemian morphologist, adheres to the 
view put forward by Strasburger 3 that the production of endosperm 
is “ a continuation of the original process of endosperm-formation ivhicli 
had been interrupted by the early appearance of fertilisation, all the 
1 This view had also been expressed by Guignard in his early 
work on the embryo-sac. 
2 “ Ueber den phylogenetischen Kntwickelungsgang der 
Bliithe, &c.Part II., p. 207 (Sitzungsbericlite der konigl. 
boll 111. Gesellschaft der Wissenscliaften in Prag, 1900). 
3 pie Angiospernien and die Gymnospermen, 1879. 
