OF BOTANY. XXV 



257. If buds, under the same circumstances, develope without forming pedun- 

 cles, a spike is produced. 



258. Hence the only difference between a spike and raceme is, that in the former 

 the Mowers are sessile, and in the latter stalked. 



259. A spadix differs from a spike in nothing more than in the Bowers bi 

 packed close together upon a succulent axis, which is enveloped in a spatha (232). 



200. An amentum is a spike, the bracteai of which are all of equal size, and 

 closely imbricated, and which is articulated with the stem. 



201. When a bud produces flower-buds, with little elongation of its own axis, 

 cither a capilulum or an umbel is produced. 



202. The capitulum bears the same relation to the umbel as the spike to the ra- 

 ceme ; that is to say, they differ in the flower-buds of the capitulum being sessile, 

 and of the umbel having pedicels. 



203. The dilated depressed axis of the capitulum is called the receptacle. 



204. A raceme, the lowest flowers of which have long pedicels, and the upper- 

 must short ones, is a corymb. 



205. A panicle is a raceme, the flower-buds of which have, in elongating, deve- 

 loped other flower-buds. 



200. A panicle, the middle branches of which are longer than those of the base or 

 apex, is called a thyrsus. 



207. A panicle, the elongation of all the ramifications of which is arrested, so that 

 it assumes the appearance of an umbel, is called a cyme. 



208. In all modes of inflorescence which proceed from the buds of a single branch. 

 the axis of which is either elongated or not, the flowers expand first at the base of 

 the inflorescence, and last at the summit. This kind of expansion is called centri- 

 petal. 



209. When the uppermost or central flowers open first, and those at the base or 

 the circumference last, the expansion is called centrifugal. 



270. The centripetal order of expansion always indicates that the inflorescence 

 proceeds from the developement of the buds of a single branch. 



271. When inflorescence is the result of the developement of several branches, 

 each particular branch follows the centripetal law of expansion, but the whole mass 

 of inflorescence the centrifugal. > 



272. This arises from the partial centripetal developement commencing among 

 the upper extremities of the inflorescence instead of among the lower. 



273. Consequently, this difference of expansion will indicate whether a particular 

 form of inflorescence proceeds from the developement of the buds of a single branch, 

 when it is called simple, or not, when it is called compound. 



274. Whenever the order of expansion is centripetal, the inflorescence is to be 

 understood as simple; when it is centrifugal, it is compound, although in appear- 

 ance simple. This difference is often of great importance. 



275. When the order of expansion is irregular, it indicates that the mode of de- 

 velopement of the flowers is irregular also, either on account of abortion or other 

 causes. 



270. Sometimes all the flowers of the inflorescence are abortive, and the ramifi- 

 cations, or the axis itself, assume a twisted or spiral direction ; when this happens, 

 a tendril is formed ; Ex. the Vine. 



XL FLORAL ENVELOPES. 



277. The Floral Envelopes are the parts which immediately surround the stamen 

 and pistils. 



278. They are formed of one or more whorls of braclea?, and arc therefore modi 

 tied leaves (229). 



2T9. In anatomical structure they do not essentially differ from the leaves, far- 

 ther than is necessarily consequent upon the peculiar modilications of size or deve- 

 lopement to which they are subject. 



280. When the floral envelopes consist of but one whorl of leaves, they are called 

 calyx. 



281. When two or more whorls are developed, the outer is called calyx, the inner 

 corolla. 



282. There is no other essentia] difference between the calyx and enroll;!. Then 

 fore, when a plant has but one floral envelope, thai one is calyx, whatever may bi 

 its colour or degree of developement , 



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