176 
Sargant . — The Reconstruction of a Race of 
Monocotyledons are, on the whole, a far less vigorous class than Dico- 
tyledons ; as a rule their representatives are found under rather exceptional 
conditions. Thus Palms do not extend far beyond the tropics ; bulbous 
and tuberous families (Liliaceae, Iridaceae, &c.) are characteristic of Alpine 
situations and dry climates with periodical rains. Almost the only Mono- 
cotyledons which compete successfully with Dicotyledons over a wide 
range are the Grasses. 
Professor Henslow has remarked on the large proportion of small 
orders found among Monocotyledons. Considering this character, together 
with the peculiarities of distribution just mentioned, they may perhaps 
be considered as a class which has seen better days : — as survivals from 
a period in which they were more numerous and more widely spread than 
in the present geological epoch. I shall endeavour later on to show that 
such an hypothesis is not unreasonable ; if it be granted, we may look on 
living Monocotyledons as a race which has been on the whole unsuccessful 
in the struggle for existence, and in consequence maintains itself chiefly 
in situations where the local conditions are exceptionally favourable to its 
peculiar characters. 
The number of small aquatic orders found among Monocotyledons 
is easily explained by this hypothesis, for among animals and plants alike 
many ancient forms have survived by adapting themselves to life in small 
ponds or in streams where the competition for existence is less keen than 
under more genial conditions. 
A mass of observations has been collected by Professor Henslow 
to show that features characteristic of Monocotyledons occur chiefly or 
exclusively among aquatic Dicotyledons, when found in that class at all. 
Only a few of these observations can be mentioned here ; I have attempted 
to pick out the most important. 
(i) Arrest of one Cotyledon . 
The examples given are Trapa natans. Ranunculus Ficaria , and Carum 
Bulbocastanum . Of these only Trapa natans is aquatic, and it is, so far 
as I know, the only instance among aquatic Dicotyledons in which one 
cotyledon is absent or much reduced. As a rule they possess two, often 
specialized as food-storers. On the other hand, there are at least twelve 
other species of Dicotyledons distinguished by possessing one cotyledon 
only (Sargant, 72, p. 76 ). Not one of them is aquatic, but they are all 
geophilous, and most of them very highly specialized to that habit. 
(ii) Sheathing petioles. 
The leaves of Monocotyledons are commonly expanded at the base into 
a broad sheath, which encloses the bases of the younger leaves more or less 
completely. The petiole of some Dicotyledons is expanded at the base 
