CHAPTER XX 
CLASSIFICATION OF ANGIOSPERMS AND SOME 
OF THEIR FAMILIES OF MOST ECONOMIC 
IMPORTANCE 
Classification. — The Angiosperms are so numerous and vary 
so widely that their classification is not at all settled. Ray, a 
noted English botanist (1628-1705), divided the Angiosperms 
into two sub-classes — Monocotyledons and Dicotyledons — 
on the basis of the number of cotyledons. There are also other 
features which are used in distinguishing these two groups, 
such as the number of floral structures composing the flower, 
the venation of the leaves, the arrangement of the vascular 
bundles in the stem, and the presence or absence of cambium. 
Thus leaves with parallel veins, the parts of the flower in threes 
or sixes, the scattered arrangement of vascular bundles in the 
stem, and closed vascular bundles are characteristic of Mono- 
cotyledons, while leaves with net-veins, floral parts in fours or 
fives, vascular bundles arranged in a circle so as to enclose the 
pith, and indefinite growth by means of a cambium are charac- 
teristic of Dicotyledons. As to whether the Monocotyledons 
arose from the Dicotyledons, or the Dictyledons from the 
Monocotyledons is a question that botanists are not able to 
answer satisfactorily. However, recent studies of the young 
embryos of some of the Monocotyledons show that there are 
two cotyledons present, one of which is very rudimentary. 
This discovery with other structural and historical features has 
given rise to the view that the monocotyledonous condition 
arose from the dicotyledonous condition through the suppres- 
sion of one of the cotyledons. This means that the growth 
which first becomes evident at the top of the developing embryo 
as two points, each of which develops into a cotyledon in Dicoty- 
ledons, became concentrated into the development of only one 
point which consequently develops the single large cotyledon 
characteristic of Monocotyledons. 
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