MORPHOLOGY 37 



origin ; or the stipules may completely encircle the stem, and thus 

 form a sheath (OCHREA) about the younger undeveloped leaves. 

 This sheath-like fusion of the stipules may be easily observed on the 

 India-rubber tree (Ficus elastica), now so commonly grown as a 

 decorative plant. In this case the stipular sheath is burst by 

 the unfolding of each new leaf and pushed upwards. In the 

 Polygonaceae the stipular covering is similarly torn apart by the 

 developing leaves, but remains on the stem in the form of a 

 membranous sheath. 



Scale Leaves possess a simpler form than foliage leaves, and are 

 attached directly to the stem, without a leaf-stalk. They exercise 

 no assimilatory functions, and are more especially of service as 

 organs of protection. Scale leaves exercise their most important 

 function as BUD-SCALES (Fig. 37); they are then hard and thick, and 

 usually of a brown colour. They most frequently take their origin 

 from the enlarged leaf-base ; in that case the upper leaf either does 

 not develop, or exists only in a reduced condition at the apex of 

 the scale. The true morphological value of scale leaves of this 

 nature is very evident in the bud-scales of the winter buds of the 

 Horse-chestnut (Aesculus Hippocastanum) ; for, while the outer scales 

 show no perceptible indications of an upper leaf, small leaf-blades 

 can be distinctly distinguished at the apices of the inner scales. In 

 other cases the scale leaves are modified stipules (Fig. 37), and are 

 then also derived from the leaf-base ; while, in other instances, they 

 correspond to the enlarged, but still undifferentiated, primordial leaves. 

 The bud-scales of the Oak are the stipules of leaves of which the 

 laminae are only represented by minute scales. Scale leaves, 

 usually colourless and in various stages of reduction, are found on 

 rhizomes (Figs. 23, 34), bulbs (Fig. 25), and tubers (Fig. 26). On 

 the aerial stems arising from such subterranean shoots the forma- 

 tion of similar scale leaves generally., 1 precedes the development of 

 the foliage leaves, with which they are connected by a series of 

 transitional forms. 



Braeteal Leaves resemble scale leaves in form, and have a 

 similar origin (Fig. 34 hb). They act as subtending leaves for the 

 floral shoots, and are termed BRACTS. They are connected with 

 foliage leaves by intermediate forms (Fig. 38). Though they are 

 not infrequently green they may be otherwise coloured, or even 

 colourless. 



Floral Leaves. The modified leaves which form the flowers of 

 Phanerogams are termed floral leaves. In the highest development 

 attained by a phanerogamic flower (Fig. 39), the successive floral 

 leaves are distinguished as sepals (&), petals (c), stamens (), and 

 carpels (<?). In form the sepals and petals approach the bracts. 

 In most cases the sepals are green and of a firm structure ; the 

 petals, on the other hand, are more delicate and variously coloured. 



