136 PLANTS WITH TRAPS AND PITFALLS TO EXSXARE ANIMALS. 



underside or back of the leaf is really a portion of the superior surface. For as 

 a matter of fact each of these thick squamiform leaves is rolled back, and in it tin- 

 following parts may be distinguished : first, the place of insertion on the stem 

 (fig. 25 3 ) which is relatively small ; secondly, the portion taken on cursory 

 examination to be the whole upper surface of the leaf, and consisting of an 

 obliquely ascending blade limited by a sharp edge or border; next, starting from 

 this sharp border, the part, which, owing to its being suddenly bent down at an 

 acute angle and falling away steeply, is usually taken for the lower surface of 

 the leaf, but which belongs, in point of fact, to its upper surface; fourthly, the 

 free extremity of the leaf in the form of an involute limb; and fifthly, the true 

 dorsal (under) part, which is very small relatively to the whole, and is not visible 

 until the involute tip is removed. Owing to the involution of the apex or tip, a 

 canal or rather a recess is formed and runs across beneath the leaf, close under the 

 place where the latter is joined to the stem (see fig. 25 2 ). From five to thirteen 

 (usually ten) chambers open into this recess through a series of little holes. They 

 are excavations in the thickness of the scales and are probably, in this form at 

 any rate, unique in the realm of plants. To solve the problem of their significance 

 in relation to the life of the plant, and to its absorption of nutriment in particular, 

 it is necessary to examine them somewhat more in detail. This we will now 

 proceed to do. 



The cavities, varying in number, as has been already mentioned, from five to 

 tliirteen, are situated very closely together, but are not connected laterally. They 

 are all deeper than they are broad, and have irregularly undulating walls (see 

 fig. 25 3 ). Two kinds of structures are conspicuous on the internal surfaces of the 

 walls, being raised above the ordinary epidermal cells, and projecting into the 

 cavity. Structures of the first kind are present in large numbers, and each of 

 them consists of a pair of cells in the form of a little head, borne by a short, 

 cylindrical cell serving as a stalk. The other variety, which occurs much more 

 sparsely, is composed of a comparatively large tabular cell, roundish or elliptical 

 in outline, inserted amongst the ordinary epidermal cells and only slightly raised 

 above them, and of two convex cells, forming a low dome, which rests upon this 

 base (rig. 25 4 ) as though on a salver. The walls of these cellular structures pro- 

 jecting into the cavity are comparatively thick, and when the protoplasts living in 

 the cells are stimulated, they appear to send out, through pores in the thick walls, 

 delicate filaments exactly like the protoplasmic threads which the coated Infusoria, 

 known by the name of Rhizopoda, stretch forth through the pores of their armour 

 (see fig. 25 s ). 



When small animals penetrate into the labyrinthine chambers of a l.nthrcea 

 leaf and touch the organs just described, the protoplasmic filaments are protruded 

 in rays in response to the stimulus, and lay themselves upon the intruders. They 

 act as prehensile arms in holding the smaller prey, chiefly Infusoria, and impede 

 the motion of larger animals so as to cut off their retreat No special secretion has 

 been observed to be exuded in the foliar chambers of Lathrcea. But, seeing thai 



