Cuar. J.J STRUCTURE OF THE LEAVES. 5 
glands of the longer tentacles, and a broader zone near their bases, of a 
green tint. Spiral vessels, accompanied by simple vascular tissue, 
branch off from the vascular bundles in the blade of the leaf, and run 
up all the tentacles into the glands, 
Several eminent physiologists have discussed the homological nature 
of these appendages or tentacles, that is, whether they ought to be 
considered as hairs (trichomes) or prolongations of the leaf. Nitschke 
has shown that they include all the elements proper to the blade of a 
leaf; and the fact of their including vascular tissue was formerly 
thought to prove that they were prolongations of the leaf, but it is 
now known that vessels sometimes enter true hairs.* The power of 
movement which they possess is a strong argument against their being 
viewed as hairs. ‘The conclusion which seems to me the most 
probable will be given in Chap. XV., namely that they existed pri- 
mordially as glandular hairs, or mere epidermic formations, and that 
their upper part should still be so considered ; but that their lower 
part, which alone is capable of movement, consists of a prolongation of 
the leaf; the spiral vessels being extended from this to the uppermost 
part. We shall hereafter see that the terminal tentacles of the 
divided leaves of Roridula are still in an intermediate condition. _ 
The glands, with the exception of those borne by the extreme 
marginal tentacles, are oval, and of nearly uniform size, viz. about 54, of 
an inch in length. Their structure is remarkable, and their functions 
complex, for they secrete, absorb, and are acted on by various stimulants. 
They consist of an outer layer of small polygonal cells,t containing 
purple granular matter or fluid, and with the walls thicker than those 
of the pedicels. Within this layer of cells there is an inner one of 
differently shaped ones, likewise filled with purple fluid, but of a 
slightly different tint, and differently affected by chloride of gold. 
These two layers are sometimes well seen when a gland has been 
crushed or boiled in caustic potash. According to Dr. Warming, there 
is still another layer of much more elongated cells, as shown in the 
accompanying section (fig. 3) copied from his work; but these cells 
were not seen by Nitschke, nor by me. In the centre there is a group 
of elongated, cylindrical cells of unequal lengths, bluntly pointed at 
their upper ends, truncated or rounded at their lower ends, closely 
pressed together, and remarkable from being surrounded by a spiral 
line, which can be separated as a distinct fibre. 
These latter cells are filled with limpid fluid, which after long 
* Dr. Nitschke has discusssd this 
subject in ‘ Bot. Zeitung,’ 1861, p. 
241, &e. See also Dr. Warming 
(‘Sur la Différence entre les Tri- 
chomes, &c., 1873), who gives refer- 
ences to various publications. See 
also Grænland and Trécul, ¢ Annal. 
des Sc. nat. bot.’ (4th series), tom. 
iii. 1855, pp. 297 and 303, 
+ [Gardiner (¢ Proc. Royal Soc., No. 
240, 1886) has pointed out that in 
Drosera dichotoma “the gland-cells 
of the head are provided with delicate 
uncuticularised cell-walls, which are 
remarkably pitted on their upper or 
free surfaces.”—F. D.] 
