are shield-shaped, about the size of a shilling piece, 
and so very different in appearance that if they 
were plucked and shown singly to anyone who was not 
previously familiar with them, he would most likely pro- 
nounce them to have been taken from separate plants. 
Another very noticeable plant is Limnanthemum Hum- 
boldtianum, which was once very plentiful in an ugly 
trench near the Tramway terminus, but it has now en- 
tirely disappeared from the spot and of late we have 
missed its delicately fringed white flowers from all its old 
haunts. The fringed petals furnish a ready means of 
discriminating the species. 
Two other little trench plants, Salvinia auriculata and 
Azolla Caroliniana, deserve to be mentioned for the 
surprising rapidity with which they increase in our tren- 
ches. They are both free floating plants and very 
great pests in trenches, often covering the whole surface 
of the water with a pink or green carpet. 
Every one must be acquainted with the glaucous green 
rosette of Pistia stratiotes, a plant that looks like a small 
floating lettuce, but few would think of conne6ling it 
with our tannias and eddoes, yet it belongs to the same 
natural order. The flowers are small and white, and 
are borne in the axils of the leaves. 
Closely resembling the above, but readily to be dis- 
tinguished by the spongy nature and brighter green 
colour of its rosettes, is another common weed, Limno- 
bium spongia, the flowers of which are without petals and 
raised on slender stalks. 
The last of our conspicuous trench plants are the 
common water lilies, Nymphaea blanda and ampla, which 
grow abundantly in the trenches in the environs of 
