62 



THE FLOWERING PLANT. 



7.— Pitcher of Nepenthes. 



and separated by a constriction from the lamina, which is com- 

 posed of two oval halves, the margins of which are provided with 

 bristles, while the upper surface of each bears about three slender 

 highly sensitive hairs. In one of the 

 pitcher - plants, Nepenthes (fig. 27), 

 species of which occur in Madagascar, 

 Ceylon, and the East Indies, the mid- 

 rib of the simple leaf extends beyond 

 the apex of the lamina as a tendril, 

 which terminates in a lidded pitcher 

 resembling a hot- water jug in shape. 

 The bladder- wort (Utricularia) is an 

 aquatic herb, sparsely distributed in 

 British ponds and ditches. Its leaves 

 are pinnately parted into numerous 

 narrow lobes, some of which bear 

 small- stalked bladder-like structures, 

 each of which possesses an inwardly- 

 opening valve -like aperture. 

 The texture of the lamina may be either herbaceous, leathery, 

 or succulent. The first characterizes most of our common leaves, 

 which are deciduous, i.e., shed annually (p. 43). Leathery leaves, 

 capable of greater endurance, are found in evergreens, which 

 owe their name to the fact that the foliage is shed gradually, 

 so that the branches are never bare. Succulent leaves, such 

 as those of the aloe, are especially characteristic of arid climates 

 (cf. p. 27). 



The colour of the lamina is not uniform. Not to mention 

 spotted, mottled, and variegated leaves, it usually happens that 

 the upper side is of a darker green than the lower. This is 

 principally due, as we shall see, to the way in which the internal 

 green tissue is arranged. But the colour is also dependent on 

 the nature of the surface. This may be glabrous, especially in 

 evergreens, or more or less hairy, and in the latter case it is usual 

 for the hairs to be more numerous on the under side, giving this 

 a whitish hue. Silverweed (Potentilla anserina) is a beautiful 

 example, and the same thing is seen to a less extent in wallflower, 

 buttercup, <kc. Some leaves are of a bluish-green colour, and 

 this may be due to the presence of wax, as in the garden poppy. 

 Glandular hairs are frequently found on the lamina, and these 

 very often secrete a fragrant oil, as in lavender, where short 

 glandular hairs are mixed with larger branched non-glandular 

 ones. The perfume patchouli is obtained from a similar source, 

 and the odour of sweet-briar is also due to such hairs. Stinging 

 hairs may be present on the lamina (petiole and stem) as in the 



