SCALE-LEAVES, FOLIAGE-LEAVES, FLORAL-LEAVES. 637 



the peculiar conditions of the enviroument, has also been repeatedly discussed, and 

 it is enough to remember here that the principal duties of the leaf-stalk, as the 

 support of the light-needing green blade, are to turn and twist it, to raise and 

 lower it, to bring it always into a position where it will be f)roperly illuminated; 

 to keep it in that position in spite of storm and tempest. The chief function of 

 stijjules consists in screening young and tender leaves — not yet emerged from the 

 bud — from excessive illumination, and protecting them from too much loss of heat 

 on clear nights. The stipules in many cases actually serve as bud-scales, as may 

 be seen in the fig-tree, where the tiny leaf -blades are rolled up together and 

 inclosed in the spathe-like stipules. When this is the sole function of the stipules, 

 they become detached after the unfolding of the leaves wrapped round by them. 

 Consequently, shortly after the unfolding of the foliage of oaks, beeches and other 

 trees, the floor of the forests formed by these trees is strewn with enormous 

 quantities of fallen stipules. When the stipules persist at the sides of the leaf- 

 stalk and become green, there can be no doubt but that they supplement the green 

 leaf-blades in their function, and like them manufacture organic suljstances from 

 inorganic food. In the Woodruff, Bed-straw, Madder {Asperula, Galium, Rubia) 

 the stipules actually possess the same size, shape and colouring as the blades of the 

 real foliage -leaves, and thus a star of green leaf -structures is formed, to which 

 these plants owe their name of Stellatas. In the Pansy ( Viola tricolor) and 

 numerous species of violet allied to it, the stipules are green and sometimes larger 

 than the leaf -blade, at the base of which they occupy a subordinate position. 



A peculiar formation is observed in the Yellow Vetch (Lathyrus Aphaca), a 

 common weed in the fields of Southern Europe, though not so frequent in England. 

 In this plant the leaves are completely transformed into tendrils which serve as 

 climbing organs; the two stipules which stand at the base of the metamorphosed 

 leaf have, on the other hand, assumed the function of leaf-blades; they are very 

 large, provided with green tissue, of arrow-like or lanceolate contour, and at a 

 cursorj^ glance may be easily taken for leaf-blades. It has already been mentioned 

 on \>. 335 that a like modification of function occurs in many Australian acacias, 

 the foliage-leaves of which are devoid of green blades whilst the leaf-stalks are 

 developed as green, flattened, outspread organs, the so-called phyllodes. 



In all these cases we have only treated of the most important function of 

 foliage-leaves, that is, the formation of organic materials from inorganic food in 

 sunlight. But as mentioned previously, the foliage -leaves of many plants are 

 assigned other functions, which again require certain peculiar adaptations, and 

 contribute not a little to the great variety in the form of this organ. One series 

 of these metamorphoses, viz. the transformation of the leaf-blades and leaf-stalks 

 into traps and digestive organs in insectivorous plants; the metamorphosis of 

 Ijlades, leaf-stalks, and stipules into weapons; and the development of furrows and 

 channels on different parts of the foliage-leaves for the irrigation of rain-water; 

 and finally the transformation of foliage-leaves into mere scales, as in the switch 

 plants, &c. — all these have alreadj' been fully treated of in earlier chapters. But 



