XXIV INTRODUCTION. 



Plantagineae, Cyperaceoe, and Gramineae, have dense simple imbricated 

 spikes; all Betulineae, Cupuliferae, and Salicineje, 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 of 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 characterised, such as Salicineae, Piperaceae, 

 Saururese, &c. ; but in Betulineae it is present in the male flowers, 

 and in Euphorbia itself, among Monochlamydeae, it is wholly wanting. 

 These exceptions do not, however, affect the general importance of 

 characters derived from its presence or absence. If it is unaccom- 

 panied by the corolla, plants are said to be Monochlamydeous; and 

 this is a point of very uniform value. I know of no true Monochla- 

 mydeous orders in which the presence of a corolla forms an exception, 

 unless the faucial scales of Thymelseae are considered the rudiments 

 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 monosepalous, and in Chenopodeae it is as regularly 

 polysepalous ; but in Caryophylleae both forms are observable. — The 

 number of sepals is sometmies a character of importance, as in 

 Cruciferte, in which they are always 4, in Papaveraceae, 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 Guttiferac they vary from 2 to 6 ; in Homalineae 

 from 5 to 15; and in SamydesB from 3 to 7. — The asstivation of the 

 calyx is always to be well considered, as certain forms are often 

 among the best known indications of affinity. Malvaceae, TiliaceaB, 

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

 clusively valvate among polypetalous dicotyledons with hypogynous 

 stamens ; Ternstromiaceae have the sepals constantly imbricated in 

 a particular way ; Vites have the lobes of the calyx distinct and 

 wide apart from a very early period of their existence: but in 

 Penaeaccac both valvate and imbricate aestivation exists. — In some 

 plants the sepals are all of equal size ; in others they are very 

 unequal either in form, direction, or texture; in the former case they 

 are said to be regular, in the latter irregular, and by this difference 



