CHAP. I. STRUCTURE OF THE LEAVES. 7 



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 

 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 traced close up to the spiriferous* cells. Their development 

 bas been described by Dr. Warming. Cells of the same kind 

 have been observed 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 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 Droseracea3. 



The extreme marginal tentacles differ slightly from the others. 

 Their bases arc 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 em- 

 bedded on the upper surface of the pedicel, instead of standing 

 at the apex. In other respects they do not differ essentially 

 from the oval ones, and in one specimen I found every possible 

 transition between the two states. In another specimen there 

 were no long-headed glands. These marginal tentacles lose 

 their irritability earlier than the others ; and when a stimulus 

 is applied to the centre of the leaf, they are excited into action 

 after the others. When exit-off leaves are immersed in water, 

 they alone often become inflected. 



The purple fluid or granular matter which fills the cells ot 

 the glands differs to a certain extent from that within the 

 cells of the pedicels. For when a leaf is placed in hot water or in 

 certain acids, the glands become quite white and opaque, whereas 



2 



