and Affinities of Trapella. 103 
in surface view ; the pore is formed by the separation of a 
number of cells, which later on all break down (i. e. the ring of 
cells surrounding the pore), leaving a large hole. The water- 
glands of the submerged leaves are similar in structure, though 
not quite so large. Fig. 63 c is a surface view of two teeth of 
a submerged leaf, showing the water-glands and the vascular 
bundles running to them. In the glands of the submerged 
leaves I was never able to find a mere water-pore ; there was 
always a hole, leading from the epithem to the exterior, formed 
by the breaking down of a number of epidermal cells. This 
occurrence of water-glands, on the submerged as well as on 
the floating leaves of Trapella , is of interest, but it is not 
unique, as in Callitriche 1 a similar state of things has been 
described. 
The general arrangement of the mesophyll in the two forms 
of leaves differs. In the floating leaves there are some three 
layers of palisade-cells towards the upper face, and spongy 
parenchyma below. Running in the mesophyll are the small 
vascular bundles with very well-developed parenchymatous 
sheaths and collaterally arranged elements. 
In the submerged leaves no palisade-tissue is present — the 
mesophyll having a reduced structure. 
Affinities. 
From the account of the morphology of the plant, it will be 
seen that some difficulty must attend the reference of Trapella 
to any existing Natural Order. There can however be little 
doubt of its belonging to the bilabiate Monopetalae, its more 
than half-inferior ovary, a rare thing in that series, not- 
withstanding 2 . The group of the Labiatiflorae contains a 
number of Orders, many of which are not well-defined. In 
1 v. De Bary, Comp. Anat. Veg. Organs, &c., Eng. ed. p. 53. 
2 It will I think be acknowledged that Trapella must find its allies among the 
Monopetalae with superior rather than with those with inferior ovaries. In the 
latter possibility Caprifolmcecve is the only group to which it might be technically 
allied. In the discussion which follows I am assuming it to be allied to plants 
with superior ovary. 
