INTRODUCTION. 



lix 



in the following Work spoken of these points of structure according to the 

 received opinions of botanists. 



The second floral envelope we call the Corolla. It consists of a number 

 of leaves equal to those of the calyx, and alternating with them ; in addi- 

 tion to which they are usually coloured. — If the corolla is present, a plant 

 is said to be dichlamydeous, and much importance is attached to this pecu- 

 liarity ; far more, I think, than it deserves. It constantly separates plants 

 having much natural affinity, as Euphorbiacese far from Rhamneae, Ama- 

 rantaceae widely from Illecebreae ; and it is also one to which there are 

 numberless exceptions. This is, however, not the case with monopetalous 

 dicotyledons, Primulaceae and Oleaceae being almost the only instances of 

 orders among those which are truly monopetalous, containing apetalous 

 genera. — The difference between a monopetalous and a polypetalous corolla 

 is this, that in the one the leaves out of which the corolla is formed are 

 distinct, and in the other united. Great value is attached to this, and it 

 is in fact a difference of first-rate importance : thus, all Ranunculaceae, 

 Rosacea^ Cruciferae, Papaveraceae, Terebintaceae, and a multitude of 

 others, are, without exception, polypetalous ; and all Boragineae, Labiatae, 

 Scrophularineae, and Bignoniaceae, are equally, without exception, mono- 

 petalous : but in the polypetalous orders of Crassulaceae, Diosmeae, Poly- 

 galeae, Ternstromiaceee, &c, there are many monopetalous genera ; and 

 monopetalous Caprifoliaceae are usually associated with Hedera and Cor- 

 nus, which are as much polypetalous as any other plants. — The aestiva- 

 tion of the corolla rarely furnishes characters connected with the natural pro- 

 perties of plants ; nevertheless, Compositae are essentially distinguished by 

 their valvate, and Asclepiadeae and Apocyneae by their contorted aestivation, 

 an exception to the one existing only in the genus Leptadenia, and in the 

 other in Gardneria. The aestivation of both calyx and corolla has as yet 

 received too little attention for its value to be judged of generally. — The 

 regularity or irregularity of the corolla is most commonly important : thus, 

 Orchideae, Polygatleae, Bignoniaceae, Fumariaceae, are irregular without 

 exception ; the regular flowers of Boragineae will almost distinguish them 

 from Labiatae, which have as frequently irregular ones ; yet Echium in 

 Boragineae is irregular, and Caprifoliaceae exhibit all the gradations from 

 a corolla of the most irregular form to one of the most perfect symmetry. 

 In Compositae both are found continually in the same head ; and Lobe- 

 liaceae, which may be almost always distinguished from Campanulaceae by 

 their irregularity, become nearly regular in Isotoma. — The venation of 

 the petals is scarcely ever employed for distinction, little being at present 

 known of it. Compositae are distinguished by the peculiar arrangement 

 of the veins of their corolla ; and they are always oblique in Hypericineae. 



From within the corolla arise certain metamorphosed leaves, which are 

 called the stamina and pistils. From the manner in which they are com- 

 bined, good characters may sometimes be derived, but frequently no cha- 

 racters at all. Thus, Xanthoxyleae are known from Diosmeae and Tere- 

 bintaceae by their diclinous flowers; all Euphorbiaceae, Begoniaceae, 

 Amentaceae, Coniferae, Myriceae, are diclinous. But Vites, Gramineae, 

 Cyperaceae, Chenopodeae, Umbelliferae, and even Ranunculaceae contain 

 monoclinous and diclinous genera ; and it is familiar to every one, that 

 flowers of both these kinds stand side by side in Compositae. 



