On Some Stages 171 the Life History of Gnetum. 
239 
spermzellbildung um die freien wandstdndigen Kerne hegonnen.'''' A similar 
formation of endosperm before fertilisation may also take place in 
G. UumpManum, for in his earlier paper Karstein figures * a sac of this 
species unmittelbar vor dem eintreffen des Pollenschlauches," in which the 
chalazal region shows the " anfang der Endospermbildung " — no less than 
13 multinucleate cells appearing in the section. It is clear, therefore, that 
in these two of Karsten's species endosperm-formation does sometimes 
precede fertilisation. 
In Lotsy's account of G. Gnemon he describes the sac awaiting fertilisa- 
tidn as " a sac constricted at some point below the middle, the lower end up 
to the constriction containing a pro thallium, the part al)ove it containing a 
large number of free nuclei. In this stage the embryo-sac can be fertilised, 
no further changes occur." f 
The last sentence has frequently been interpreted as meaning that the 
formation of endosperm to the extent described X is, in this species, constantly 
antecedent to fertilisation. This, however, was not Lotsy's meaning, for on 
the same page he says, " this prothallium, as I will call it, is undoubtedly 
present, at least in many cases, before fertilisation has taken place." And 
elsewhere § he states that " if no fertilisation occurs the embryo-sac becomes 
filled with endosperm." Lotsy therefore leaves it an open question whether 
or not fertilisation may occur in G. Gnemon before endosperm-formation 
has commenced. A comparison of his figures 34 and 36 makes it clear that 
the amount of endosperm at the time of fertilisation is not constant. 
According to Karsten, therefore, fertilisation may occur in G. ovalfolkim 
and G. Etimphianum after the chalazal region of the sac is filled with endo- 
sperm, as, perhaps usually, is the case in G. Gnemon. Since in the latter 
species endosperm-formation proceeds towards the micropylar end of the sac 
if fertilisation is not effected, it is highly probable that this may take place 
also at a later joeriod than those described by Lotsy, who does not definitely 
assert that it never precedes the formation of endosperm in the chalazal 
region. Coulter, || on the other hand, states that in this same species all the 
sac-nuclei are free when fertilisation occurs. We have abundant confirma- 
tion of the accuracy of Lotsy's account, but Karsten's statements and, more 
particularly some new facts now established for G. africamim, make it 
probable that the condition described by Coulter may also occur ; in other 
words, that both accounts are correct for G. Gnemon. The evidence as it 
stands seems to indicate that in any species fertilisation does not necessarily 
take place at any particular stage in the formation of the endosperm, though 
* Karsten, 1892, figs. 9, 9 a (here called G. edule, see Karsten, 1893 b, p. 338). 
t Lotsy, 1899, p. 93. 
X Cf. Lotsy, loc. cit., figs. 34, 36, etc. 
§ Loc. cit., p. 107. 
1] Coulter, 1908, p. 44. 
