INTRODUCTION. 



lvii 



Salicineae, Magnoliaceae, Artocarpese, and many others : a particluar modi- 

 fication of thein, called the ochrea, is the peculiar distinction of Polygoneae; 

 and they are universally absent in Myrtaceae properly so called, Guttifera?, 

 Gentianes, Malpighiaceee, and many others. The orders Cistineae, Saxi- 

 frages, and Loganies, are among the very few cases in which genera 

 exist both with and without stipulae. (See Von Martius Nov. Gen. et Sp. 

 2. 135.) 



The little starved leaves found at the base of many flowers, and techni- 

 cally called Bracte.^e, are rarely employed as distinctions of orders, offer- 

 ing scarcely any modifications of importance. In Cruciferae they are never 

 present, and in Marcgraaviaceae they are usually hollow, being folded 

 together by their two edges, like the leaves of which carpella are formed. 



Forms of Inflorescence are occasionally, but not often, found cha- 

 racteristic of particular tribes. Thus all Composite, Calycereae, and 

 Dipsaceae, have their flowers in heads ; all Umbelliferae bear umbels ; all 

 Labiates have axillary cymes called verticillastri ; all Plantagineae, Cype- 

 racete, and Gramineae, have dense simple imbricated spikes ; all Betulineae, 

 Cupuliferae, and Salicinea 1 , bear amenta or catkins ; and most Coniferae 

 have a strobilus or cone ; in the latter, however, the flowers are sometimes 

 solitary, as in Taxus, and then the usual form of inflorescence is departed 

 from. 



The outer envelope of the flower, called the Calyx, is used in a variety 

 cf ways to distinguish orders ; but the characters it affords are far from 

 being of equal or uniform importance. Its absence implies the absence of 

 the corolla also, which cannot possibly be present when the calyx is away, 

 unless, as in Compositae, it is obliterated by the pressure of surrounding 

 bodies. By its absence all the orders called Achlamydeous are character- 

 ized, such as Salicineae, Piperaceas, Saurureas, &c. ; but in Betulineae it is 

 present in the male flowers, and in Euphorbia itself, among Monochla- 

 mydeae, it is wholly wanting. These exceptions do not, however, affect 

 the general importance of characters derived from its presence or absence. 

 If it is unaccompanied by the corolla, plants are said to be Monochlamy- 

 deous ; and this is a point of very uniform value. I know of no true 

 Monochlamydeous orders in which the presence of a corolla forms an 

 exception, unless the faucial scales of Thymelaeaeare considered tie rudi- 

 ments of a corolla. — The sepals or leaves of which it is composed are 

 either distinct or combined ; and from this circumstance characters are 

 sometimes advantageously derived. Thus, in Sclerantheae the calyx is 

 always monosepaious, and in Chenopodeae it is as regularly polysepalous ; 

 but in Caryophylleae both forms are observable. — The number of sepals is 

 sometimes a character of importance, as in Cruciferae, in which they are 

 always 4, in Papaveracea-, which have never more than 2, and in the 

 greater part of Endogenous plants, which have usually 3. This character, 

 however, requires to be used with circumspection, as there are many more 

 instances of the number of sepals being variable than regular. Thus in 

 Lineae and Malvaceae they are 3-4-5 ; in Guttiferae they vary from 2 to 6; 

 in Homalineee from 5 to 15 ; and in Samydeae from 3 to 7. — The aestiva- 

 tion of the calyx is always to be well considered, as certain forms are 

 often among the best known indications of affinity. Malvaceae, Tiliacea?, 

 Elaeocarpeae, Tremandreae, Sterculiaceae, and Bombaceae, have it exclu- 

 sively valvate among polypetalous dicotyledons with hypogynous stamens; 

 Temstrbmiaceae have the sepals constantly imbricated in a particular way ; 



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