9 6 Oliver . — (9/z Structure , Development , 
being entirely closed by the powerfully developed integument 
(/#£. czV. p. 119), and allows the embryo-sac as it elongates to 
make its way some little distance up the micropyle — the 
cushion of cells being driven like a root-cap in front of it. 
In Trapella such an apical cushion is not developed, which 
perhaps accounts for the difficulty in recognising the mi- 
cropyle in any but the youngest stages. 
Fischer points out ( loc . cit. p. 120) how Hippuris displays 
monopetalous characters in the development of its ovule. 
Besides being similar to Trapella in these, it seems that a 
considerable space at the top of the embryo-sac in Hippuris 
is left unoccupied by endosperm h This region does not 
enlarge or form the well-marked tubercle found in Trapella , 
but we see in Hippuris 2 a state of things which may have 
existed in the group of plants from which our type has 
sprung. In many Monopetalae, indeed, considerable space 
is left, in the synergidal region, unoccupied by endosperm ; and 
in several genera, Lathraea , Pedicular is , Lamium , Veronica , 
&c., there arise from this upper region appendages and caeca 
of an extraordinary nature ; these make their way in amongst 
the tissues of the ovule. It would seem that when the 
synergidal region is left unoccupied in this way, there is a 
proneness to singular developments of one sort or another. 
In Trapella the cap-cells normally all lie below, i. e. at the 
chalazal end of, the embryo-sac, and not at its micropylar 
end. It is the uppermost cell of the row which becomes the 
embryo-sac 3 . This state of things is only paralleled, to my 
knowledge, in Rosa livida , described by Strasburger 4 and 
A. Fischer 5 . In this plant Strasburger found often the second 
1 Vide figures to Unger’s paper, in Bot. Ztg. 1849. 
2 As will be shown later, the vascular cylinder in the stem of Trapella much 
resembles that in Hippuris. 
3 In one ovule of Trapella only, I found that the second cell of the row became 
the embryo-sac. 
4 Strasburger, Angiospermen und Gymnospermen, pp. 15-16. 
5 A. Fischer, Zur Kenntn. d. Embryosackentwicklung, & c., in Jenaische 
Zeitschrift, Bd. xix (1880), p. 120. 
In Atherurus attenuatus ( Aroideae ) as figured by B. Jonsson [Om embryosac- 
kens utvecklung hos Angiosperna, Tab. viii. fig. 12, in Lund’s Universitets Ars- 
