248 
Transactions of the Royal Society of South Africa. 
The nuclei which, in G-netum and Welwitschia, fuse to form the nuclei 
of the primary endosperm-cells are potential gametes which lose this 
potentiality by fusing. This statement rests upon the following evidence : 
1. All the nuclei present in the sac at the end of the free nuclear 
condition are alike in all visible characters and reactions and in origin, 
from which they are equally distant, i. e. they are all of the same 
nuclear-generation. 
2. Each sao-nucleus follows one of three courses, viz. (1) it becomes 
fertilised, (2) it fuses with other sac-nuclei to form a primary endo- 
sperm nucleus, (3) it does neither, in which case it participates no 
further in the life-history.* 
3. In some species of G-netum (G. africannm, G. ovalifolium, G. 
Rum^hianum) , fertilisation may take place while all the sac-nuclei are 
still free. In this case, according to Karsten,t jeder einzelne der 
sfimmtlichen kerne des Embryosackes gleich geeignet als Eikern zu 
fungiren." In Welwitschia, under some circumstances, all the sac- 
nuclei may remain free % and in their appearance and reactions resemble 
those which are fertilised. 
4. All the sac-nuclei may participate in the endosperm fusions, 
in which case fertilisation is of course impossible. This occurs not 
uncommonly in Grnetum and occasionally in Welwitschia. In G-netum 
it is due to the late arrival of the pollen-tube (p. 240), in Welwitschia 
to causes which interfere with the normal growth of the sac in its early 
stages. § 
5. In Welwitschia the gametes in the embryo-sac tube may fuse to 
form a fusion-nucleus in all respects like that of a uninucleate endo- 
sperm-cell. || A small tissue of seven cells seen in an embryo-sac tube^ 
is interpreted as an endosperm formed by the division of such a 
nucleus. 
If, then, both in G-netum and Welwitschia, all the sac-nuclei may 
participate in the endosperm-fusions while under other circumstances some 
of them become fertilised ; if, further, all the sac-nuclei are potentially 
sexual, as is asserted by Karsten for Gnetum, and as seems to be indicated 
for Welwitschia by the abnormal case referred to in § 3 above ; while in both 
cases they are all equal in origin, descent, and visible characters, the state- 
* Viz. The unfertilised gametes in the enibryo-sac-tubes of Welwitschia and 
Lhose micropylar nuclei of Gnetum which are not fertilised and are " crowded out " 
from the endosperm-fusions (fig. 25, a, b). Cf. Lotsy, 1899, fig. 44, W.o.E. 
t Karsten, 1893, p. 357. 
X Pearson, 1909, p. 353. 
§ Pearson, 1909, p. 354. 
II Pearson, loc. ext., figs. 30 a, b. 
IT Pearson, loc. ext., fig. 37 a, cf. fig. 37 b. 
