Chap. I.] STRUCTURE OF THE LEAVES. $ 



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 primordially as glandular haire, 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 ex- 

 tended 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 

 g^ 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,* 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 ofles, like- 

 wise filled with purple fluid, but of a slightly different tint, and 

 differently affected by chloride of gold. These two layers are some- 

 times 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 

 immersion in alcohol deposits much brown matter. I presume that 

 they are actually connected with the spiral vessels which run up 

 the tentacles, for on several occasions the latter were seen to divide 

 into two or three excessively thin branches, which could be trdced 

 close up to the spiriferous cells. Their development has been de- 

 scribed by Dr. Warming. Cells of the same kind have been ob- 

 served in other plants, as I hear from Dr. Hooker, and were seen 

 by me in the margins of the leaves of Pinguicula. Whatever their 

 function may be, they are not necessary for the secretion of the 

 digestive fluid, or for the absorption, or for the communication of a 

 motor impulse to other parts of the leaf, as we may infer from the 

 structure of the glands in some other genera of the Droseraceae. 



The extreme marginal tentacles differ slightly from the others. 

 Their bases are broader, and, besides their own vessels, they receive 

 a fine branch from those which enter the tentacles on each side. 

 Their glands are much elongated, and lie embedded on the upper 

 surface of the pedicel, instead of standing at the apex. In other 



[Gardiner (' Proc. Roynl provided with delicate nncntlcu- 

 Soc.,' No. 240, 188C) han pointed Inrlsed cell-wallR, which are re- 

 out that In DroMrra dichotomn markably pitted on their upper 

 " the gland-cells of the head are or free surface*." F. D.] 



