8S 
and Affinities of Trapella. 
leaf-axil, so that if the fruit be disturbed in any way it 
breaks off The fruits offer every opportunity for distribution, 
with their clinging, coiled appendages, and it is surprising 
that our plant has so circumscribed a distribution, contrary 
to what is usual amongst aquatics apparently by no means 
so well -furnished as Trapella . 
Cleistogamic flowers . — The examination of several complete 
specimens of Trapella does not fail to show not only the 
presence of fruits in the axils of the floating, but also some- 
times in those of the submerged leaves which can never have 
been exposed to the air. This at once suggests the presence 
of cleistogamic 1 , in addition to normal flowers, as indeed 
proves to be the case. Careful investigation of the leaf-axils 
demonstrates the presence of minute unopened flowers about 
2-3 mm. in length, in the axils of many of the submerged 
leaves. These are cleistogamic flowers, and are at no time 
open. The calyx remains tightly folded over them and the 
corolla is reduced, and, so far as I could ascertain, two fertile 
anthers are developed, but in most cases these parts were 
disorganised. The stigma is here sessile on the top of the 
ovary (Fig. 21); in this lies their chief structural difference 
from normal flowers. The pollen is applied directly on to 
the stigma from the anthers. The cells of the ovary, insertion 
and number of ovules, & c., are quite similar in both forms, 
as also is their further history after fertilisation. Hence in 
order to distinguish whether any fruit has been cleistoga- 
mically or normally produced it must be noted, (1) whether 
it comes from the axil of a submerged or floating leaf; (2) 
whether it is pedicellate or almost sessile ; (3) whether its 
stigma is sessile on the top of the ovary or not. No. 1 is 
not however absolute, as I have not unfrequently found 
cleistogamic flowers in the axils of floating leaves, even of 
1 Cleistogamic flowers are well known in many aquatic plants : Darwin men- 
tions (Forms of Flowers) instances in Ranunculus aquatilis, Alisma natans , 
Subularia aquatica , Illecebrum verticillatum, Menyanthes , Euryale and Hottonia 
infiata (Torrey in Bull. Torrey Botan. Club, vol. ii. p. 22). In none of these 
would there appear to be any modification of structure, other than a mere reduction 
of parts due to their remaining closed. 
