MORPHOLOGY 



33 



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 Hi]jpo<ustanum) ; 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, and are then also derived 

 from the leaf-base ; while, in other instances, they themselves form 

 the enlarged, but still undifferentiated, primordial leaves. The bud 

 scales of the Oak are the stipules of leaves in which the laminae are only 

 represented by minute scales. Scale leaves, usually colourless and in 

 various stages of reduction, are found on rhizomes (Fig. 21), bulbs 

 (Fig. 23), and tubers (Fig. 24). On the aerial stems arising from such 

 subterranean shoots the formation of similar scale leaves generally 

 precedes the development of the foliage leaves, with which they are 

 connected by a series of transitiortal forms. 



Bracteal Leaves resemble scale leaves in form, and have a similar 

 development. They act as subtending leaves for the floral shoots, 

 and are termed bracts. They are connected with foliage leaves by 

 intermediate forms. Though they are not infrequently green they 

 may be otherwise coloured, or even altogether 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. 32), the successive floral leaves 

 are distinguished as sepals 

 (k), petals (c), stamens (a), and 

 carpels (g). In most cases the 

 sepals are green and of a firm 

 structure ; the petals, on the 

 other hand, are more delicate 

 and variously coloured. The 

 stamens are generally filament- 

 ous, and produce the pollen 

 in special receptacles. The 

 carpels more closely resemble 

 scale leaves, and by closing to- 

 gether form receptacles within 

 which the ovules are pro- 

 duced. The stamens and 

 carpels of Phanerogams corre- 

 spond to the spore-bearing 

 leaves of the Vascular Crypto- 

 gams. Such spore-bearing leaves are termed sporophylls, and even 

 in the Vascular Cryptogams exhibit a greater or less departure from 

 the form of other foliage leaves. It is evident that the scale and 

 bracteal leaves are to be considered as rudimental foliage leaves, not 



Fig. 32. — Flower of Paeonia peregriaa. Tc, Sepals ; c, 

 petals ; a, stamens ; </, carpels. Part of the sepals, 

 petals, and stamens have been removed to show 

 the pistil, consisting of two separate carpels. (Half 

 nat. size.) 



