LEAVES SERVING SPECIAL OFFICES. 



115 



be taken for the leaf-blade, the part below would be a broadly- 

 winged foliaceous petiole. If the latter be the true blade, the 

 apparatus in question must be reckoned as a peculiar terminal 

 appendage. Both are moderately green, and act as foliage. 

 The specially endowed terminal portion acts also in a decidedly 

 animal-like manner. When either of the three or four slender 

 bristles of the upper surface are touched, the trap suddenly 

 closes, by a movement ordinarily quick enough to enclose and 

 retain a fly or other small insect. The intercrossing of the stout 

 marginal bristles detains the captive, unless it happens to be 

 small enough to escape by the intervening little openings. 

 Otherwise, the sides soon flatten and are brought firmly into 

 contact, and a glairy secretion is poured out from numerous 

 immersed glands : this, with the extracted juices of the macerated 

 insect, is after some time reabsorbed ; the trap, if in a healthy 

 condition, now re-opens and is read} r for another capture. For 

 references to the now copious literature of this whole subject, and 

 for its plrysiological treatment, the succeeding volume should be 

 consulted. 



225. Leaves for Storage. Nutritive matter is stored in leaves 

 in many cases, and not rarely in leaves which at the 

 same time are subserving the purpose of foliage. 

 This occurs in all fleshy leaves, to a greater or less 

 extent, according to the degree of thickening or 

 accumulation. The leaves of the Century Plant 

 or Agave, for instance, are green and foliaceously 

 efficient at the surface, while the whole interior is 

 a store-house of farinaceous and other nutritious 

 matter, as much so as is a potato. The leaves 

 of various species of Aloe, Mesembryanthemum, 

 Sedum, and other " succulent" plants (in which 

 a large part of the accumulation is water) are not 

 rarely so obese as to lose or much disguise the 

 foliaceous appearance. Sometimes one portion of 

 a leaf is of normal texture and use, while another 

 is used as a reservoir for the nourishment which the 

 foliaceous part has produced. Fig. 232, a leaf from 

 the bulb of White Lily, the base of which forms 

 one of the bulb-scales, is an instance of the kind. 1 The most 



1 In Dicentra Cucullaria and (more strikingly from the sparseness of the 

 grains) in D. Canadensis, the matter elaborated in the much dissected blade is 

 conveyed to the very base of the long petiole, and there deposited in a con- 



FIG. 232. A radical leaf of the White Lily, with its base thickened into a bulb-scale, 

 which is cut across to show its thickness. 



