THE FLOWERING PLANTS, EES 
the development of its subordinate groups. The flowering 
plants of this class generally possess, as their name indicates, 
two seed lobes or germ leaves (cotyledons). The number of 
leaves composing its blossom is generally not three, as in 
most Monocotyledons, but four, five, or a multiple of those 
numbers. Their leaves, moreover, are generally more highly 
differentiated and more composite than those of the Mono- 
cotyledons; they are traversed by crooked, branching 
bunches of vessels or “veins.” To this class belong most of 
the leafed trees, and as they predominate in the tertiary 
period as well as, at present, over the Gymnosperms and 
Ferns, we may call the cznolithie period that of leafed 
forests. 
Although the majority of Dicotyledons belong to the most 
highly developed and most perfect plants, still the lowest 
division of them is directly allied to the Gymnosperms, and 
particularly to the Gnetacez. In the lower Dicotyledons, as 
in the case of the Monocotyledons, calyx and corolla are as 
yet not differentiated. Hence they are called Apetalous 
(Monochlamydez, or Apetalee). This sub-class must there- 
fore doubtless be looked upon as the original group of the 
Angiosperms, and existed probably even during the Trias 
and Jura periods. Among them are most of the leafed trees 
bearing catkins—birches and alders, willows and poplars, 
beeches and oaks; further, the plants of the nettle kind 
—nettles, hemp, and hops, figs, mulberries, and elms; finally, 
plants like the spurges, laurels, and amaranth. 
It was not until the chalk period that the second and 
more perfect class of the Dicotyledons appeared, namely, 
the growp with corollas (Dichlamydez, or Corolliflorze). 
These arose out of the Apetalze from the simple cover of the 
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