THE FLOWERING PLANTS. I I 3 



the development of its subordinate gi'oups. 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 csenolithic period that of leafed 

 forests. 



Although the majority of Dicotyledons belong to the most 

 highly developed and most perfect plants, still the lowest 

 diAdsion of them is directly allied to the Gymnosperms, and 

 particularly to the Gnetacese. In the lower Dicotyledons, as 

 in the case of the Monocotyledons, calyx and corolla are as 

 yet not differentiated. Hence they are called Apetalous 

 (Monochlamydeae, or Apetalfe). 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 group tvitk corollas (Dichlamydege, or Corolliflorse). 

 These arose out of the Apetalse from the simple cover of the 



VOL. IL I 



