136 PLANTS WITH TRAPS AND PITFALLS TO ENSNARE ANIMALS 



underside or back of the leaf is only a portion of the superior surface. In reality- 

 each of these thick squamiform leaves is rolled back, and in it the 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 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 dorsal or inferior surface of the leaf, but which belongs, in 

 point of fact, to the front of the lamina; fourthly, the free extremity of the leaf in 

 the form of an involute limb; and fifthly, the true dorsal part, which is very small 

 relatively and is not visible until the involute tip is removed. Owing to the 

 involution of the apex, 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 these recesses through a 

 series of little holes. They are excavations in the thickness of the scales and are 

 probably, in this form at anyrate, unique in the realm of plants. These extraordi- 

 nary chambers must be described as deep excavations in the foliar substance 

 proceeding from the back of the leaf. 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. 



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

 thirteen, are situated very close 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 one 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 and is 

 altogether wanting in the folds of the wavy inner wall, is composed of a compara- 

 tively 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 (fig. 25 4 ) as though on a salver. 

 The walls of these cellular structures projecting into the cavity are comparatively 

 thick, and when the protoplasts living in the cells are stimulated, they send out, 

 through numerous 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 5 ). 



When small animals penetrate into the labyrinthine chambers of a Toothwort 

 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 that 



