136 PLANTS WITH TRAPS AND PITFALLS TO ENSNARE 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 the 
following parts may be distinguished: first, the place of insertion on the stem 
(fig. 25°) 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°). 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 
thirteen, 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°). 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 (fig. 25*) 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°). 
When small animals penetrate into the labyrinthine chambers of a Lathrea 
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 Lathraa. But, seemg that 
