I 1 2 THE FLOWERING PLANT. 



Such water-holding receptacles are generally formed by rosettes 

 of leaves, but sometimes by connate leaves, as in the teasel, 

 where the cups thus constituted also digest insects that tumble 

 into them. It is superfluous to remark that aquatic plants are 

 protected from creeping land insects by the water surrounding 

 them. 



(d.) Sticky excretions may also keep off insects. Slippery wax 

 (cf. p. 41) sometimes serves this purpose, but most commonly 

 sticky substances, excreted by the general surface of the epi- 

 dermis or by glandular hairs, play this part. The seat of the 

 secretion may be foliage leaf, stem, bract, or part of the flower. 

 The butterwort, for instance, a small plant not uncommon in the 

 marshy parts of mountainous districts, possesses a basal rosette 

 of simple leaves, slippery from the presence of a secretion. From 

 the centre of the rosette rise several scapes terminated by flowers 

 something like small violets. The excretion, to the feel of which 

 the plant owes its name, is poured out from innumerable mush- 

 room-shaped glandular hairs. As in teasel, two purposes are 

 served ; for not only are the flowers protected, but the excretion 

 can digest small insects, and the edges of the leaf are sensitive, 

 curling over such insects and holding them fast. Butterwort, 

 therefore, is an " insectivorous " plant, and, in fact, is closely 

 related to the bladder wort, previously described (p. 62). Again, 

 gooseberry has glandular hairs on the outside of the cup- 

 shaped receptacle, and Plumbago upon the calyx. A very in- 

 teresting example is found in Poh/t/mnim amphibium, a plant 

 which grows with its lower part in ditches. When there is 

 plenty of water, the stem is glabrous, but it develops glandular 

 hairs if the water dries up. These disappear again when enough 

 moisture collects to surround the base of the plant. 



(<?.) Hair structures proper and thin hair-like outgrowths of the 

 corolla, &c, are often arranged so as to prevent unsuitable insects 

 from reaching the nectar. Instances of this kind are so numerous 

 that only a few can be mentioned. A "weel" of hairs (i.e., a 

 circlet of straight flexible hairs with ends slanting inwards) is 

 often found within the tube of a gamopetalous corolla, as in dead 

 nettle, verbena, and speedwell. In passion-flower the whole 

 corona is split up into narrow threads. The way to the nectar 

 may also be blocked by tangled masses of hairs growing on 

 various parts of the flower. 



(/.) It frequently happens that foliage leaves, peduncles, bracts, 

 or else parts of the flower are so shaped or arranged as to hinder 

 the access of small insects. Opposite leaves (more rarely stipules 

 or scattered leaves) often form a kind of collar, over which in- 

 sects cannot climb from below. This is the case in many gentians. 



