118 MORPHOLOGY OF LEAVES. 



of a pair of stipules into tendrils in Smilax. At least the ten- 

 drils here occupy the position of adnate stipules. The tendrils 

 of Cucurbitaceae are peculiar and ambiguous, on account of their 

 lateral and extra-axillary position and the manner in which the 

 compound ones develop their branches. But they are doubtless 

 partly if not wholly foliar. 1 



229. Petaloid Leaves, Bracts. Certain leaves, situated near to 

 flowers, and developing little or no chlorophyll in their paren- 

 chyma, exchange the ordinary green hue and herbaceous texture 

 for the brighter colors and more delicate structure which are 

 commonly seen in and thought to characterize flower-leaves. 

 Such are said to be colored, meaning, as applied to foliage, of 

 some other color than green. As petals are the type of such 

 colored parts, they are said to be petaloid, i.e. petal-like. They 

 are like petals, moreover, in one of the purposes which these sub- 

 serve. (299.) Examples of these petaloid leaves are seen in the 

 shrubby Mexican Euphorbia called Poinsettia, in Salvia spleu- 

 dens, most species of Castilleia or Painted Cup, also in the 

 white hood of Calla and Richardia ^Ethiopica (called Calla Lily), 

 and in the four white leaves which subtend the flower-head of 

 Cornus florida, and of the low herbaceous Cornel, C. Canaden- 

 sis. (Fig. 294.) Such leaves, being in proximity to flowers, and 

 all others which are within a flower-cluster or are borne by 

 flower-stalks, receive the special name of BRACTS. More usually 

 bracts are not petaloid, but different in size or shape from ordi- 

 nary leaves, either by abrupt change or gradual transition. Not 

 uncommonly they are reduced to scales or mere rudiments or 

 vestiges of leaves, of no functional importance. 



230. Flower- Leaves. The morphology of leaves extends not 

 only to " the leaves of the blossom," more or less accounted as 

 such in common parlance, but also to its peculiar and essential 

 organs, the relation of which to leaves is more recondite. Their 

 morphology needs to be treated separately, and to be preceded 

 by a study of the arrangement of leaves and of blossoms. 



1 The most satisfactory interpretation may be that of Braun and Wytller, 

 adopted by Eichler (Bliithendiagramme, i. 304) : that the flower of Cucur- 

 bita and its peduncle represent the axillary branch, the tendril by its side 

 answers to one of the bractlets (that of the other side being suppressed), 

 and the supernumerary branch springs from the axil of the tendril. This 

 makes of the tendril a simple leaf, of which the branches are the ribs. But 

 the tendril-divisions are evidently developed in spiral order, and in vigorous 

 growths occupy different heights on the tendril-axis. This favors Naudin's 

 view, that the main tendril is cauline, and its divisions leaves. 



