Notes . 
329 
A PRELIMINARY NOTE ON THE EMBRYO-SAC OF CERTAIN 
PENAEACEAE. — The Penaeaceae form a small and rather isolated group of shrubby 
xerophytes, of doubtful affinities, entirely confined to the south-western region of Cape 
Colony. The Order has not yet been thoroughly investigated ; there are apparently 
five genera — Sarcocolla, Penaea , Br achy siphon, Endonema , Geissoloma, the last being 
placed by Engler in a separate Natural Order, Of these, I have investigated five 
species, representing the first three genera, and, as careful examination and comparison 
have revealed an exact similarity in the structure and development of their gameto- 
phytes and embryo, the following account may be taken as applicable to all three. 
The macrospore mother-cell appears to form a row of three (?) macrospores, of 
which only the lowest persists, becoming the embryo-sac. This enlarges, and its 
nucleus divides to form four daughter-nuclei, which are arranged peripherally like the 
spores of a tetrad ; an arrangement exactly the same as that described for the corre- 
sponding stage in Peperomia . 1 2 3 As the embryo-sac enlarges, a central vacuole is 
formed, and these four nuclei migrate to the parietal layer of protoplasm. Here, as in 
Peperomia , they show none of the polarity so characteristic of the usual type of 
Angiospermous embryo-sac, being irregularly distributed around the periphery of the 
embryo-sac. Usually, however, as the sac elongates two of the nuclei take up their 
position, one at or near each end, and the other two about its equator ; but even this 
slight degree of polarity is often lacking, and the nuclei, or the cell-groups resulting 
from their division, may be arranged in any manner around the embryo-sac. 
From this point the resemblance to Peperomia ceases, and here it may be noted 
that, while their embryos agree in the absence of a suspensor and in the formation of 
a spherical pro-embryo, the male gametophyte differs from that of any known Angio- 
spermous type, while in Peperomia it is quite typical. 
Each of these four nuclei now divides, and the two resultant daughter-nuclei 
again divide, so that four groups, each consisting of four nuclei, are formed, one 
group from each of the four original daughter-nuclei of the embryo-sac. Protoplasm 
now aggregates around three of the nuclei in each group, and a definite limiting layer 
— ‘ Hautschicht ’ — appears about each of the cells thus formed, while the fourth 
nucleus remains free — so that in each group there are now three cells with definite 
membrane-boundaries, and one free nucleus. Either during or after the formation of 
the ‘ Hautschicht ’ round the cells, the free nucleus of each of the four groups migrates 
to the centre of the embryo-sac. There they meet, and gradually fuse to form the 
single large definitive nucleus. 
While these nuclei are fusing, the four parietal cell-groups have each assumed 
the appearance of a typical egg-apparatus, and it would seem probable that this may 
be their true nature. The discussion of the evidence in support of this hypothesis is, 
however, better postponed until the phenomena accompanying fertilization have been 
more completely investigated. 
1 Annals of Botany, vol. xxi, p. 467 ; vol. xxii, p. 91. 
2 Lang, On the Sporogonium of Notothylas. Ann. of Bot., vol. xxi, April, 1907. 
3 Campbell, D. H., The Embryo-sac of Peperomia. Ann. of Bot., xv, pp. 103-17, 1901. 
Johnson, D. S., On the Endosperm and Embryo of Peperomia pellucida. Bot. Gaz., xxx, 
pp. T— 1 1, 1900. 
Z 
