Monocotyledons and dicotyledons pj^i 



251. Dicotyledons. — Dicotyledons form the greatest group 

 of plants in rank and in numbers, being the most higlily 

 organized, and containing about eighty tliousand species. 

 They represent the dominant and successful vegetation in 

 all regions, and are especially in the preponderance in tem- 

 joorate regions. They are herbs, shrubs, and trees, of every 

 variety of size and habit, and the rich display of leaf forms 

 is notably conspicuous. 



Two great groups of Dicotyledons are recognized, tlie 

 ArcJiichlamydecB and the Hijinpetalm. In the former tlicre 

 is either no perianth or its parts are separate (polypcta- 

 lous) ; in the latter the corolla is sympetalous. Tlie Arclii- 

 chlamydefB are the simpler forms, beginning in as simple a 

 fashion as do the Monocotyledons ; while the Sympetala3 

 are evidently derived from them and become the most 

 highly organized of all plants. The two groups each con- 

 tain about forty thousand species, but the Arcliiclilamydeffi 

 contain about one hundred and sixty families, and the 

 Sympetalse about fifty. 



(1) ArchicJilamjidea'. — In this great division of Dicoty- 

 ledons are such groups as the great tree alliance which 

 includes poplars, oaks, hickories, elms, willows, etc. ; the 

 buttercup alliance, which includes buttercups, water-lilies, 

 poppies, mustards, etc. ; the rose family, one of the best 

 known and most useful groups of the temperate regions ; 

 the pea family, by far the greatest family of the Archi- 

 chlamydere, containing aliout seven thousand species ; the 

 parsley family, or umbellifers, containing numerous useful 

 forms, and being the most highly organized familj' of the 

 Arehichlamydete. 



(2) Hiimpefnlm. — These are the highest and the most 

 recent Dicotyledons. While they contain numerous shrubs 

 and trees in the tropics, they are by no means such a 

 shrub and tree group in the temperate regions as are the 

 ArchichlamydeEe. The flowers are constantly cyclic, the 

 number five or four is established, and the corolla is 



