Chapter X — 121 — Drosera 



In the upper reach the tentacle consists of the epidermis and one 

 course of parenchyma cells surrounding a very slender vascular strand 

 which extends from the leaf system up into the gland (75 — 6). This 

 was seen by Meyen in 1837, who supposed that it entered the gland. 

 This structure led Trecul (1855) to compare the tentacle with the 

 dicotyledonous stem, and to regard the adventitious buds described 

 first by Naudin as metamorphosed tentacles. Gronland called 

 them lobes, and Schacht, projections of the leaf. On the surface 

 as part of the epidermal system there are a few small sessile glands, 

 these being found also on the general leaf surface. They formed con- 

 venient marks by which H. D. Hooker was able to record changes 

 in the length of the tentacles during movement. The widened base 

 of the tentacle has, naturally, an increasing number of parenchyma 

 cells as the general leaf surface is approached. Similarly the vascular 

 system, consisting of spiral tracheids, may here consist of two or more 

 vessels, but above there is usually found only a single strand except 

 where two may overlap. Fenner did not see any phloem, and I can 

 only support him in this (ij — 7). The single vessel sets into a dense 

 mass of thick and short tracheids occupying the middle of the gland 

 (75 — 6) which, oval in form save when on a strictly marginal tentacle, 

 sits atop the narrow neck of the stalk. Those tentacles arising from 

 the leaf margin are bilaterally symmetrical, the stalk being extended 

 under the glandular structure proper in the form of a spoon holding 

 the gland in its bowl (ij — 9, n; 16 — 1-3). Darw^in records finding 

 intermediate forms, which I have also seen. The tentacles spring- 

 ing from the surface are increasingly radially symmetrical as the 

 margin of the leaf is left, are oval, and present the following struc- 

 ture. 



The oval head of the tentacle consists of four layers of cells (75 — 

 6, 8). The innermost of these is a roughly oval mass of tracheids which 

 is connected by means of the vascular strand of spiral vessels in the 

 stalk with the system in the leaf. Surrounding this xylem mass, 

 three outermore layers cover it as a thimble, the flaring mouth of it 

 articulating with the somewhat expanded tip of the stalk. The layer 

 of cells in contact with the xylem mass is distinctly bell-shaped, and 

 was called by Fenner the parenchyma bell. The flaring wall of the 

 bell is composed of a single layer of elongated, curved cells, the ex- 

 posed ends of which come to the surface of the gland, and whose cuti- 

 cle is continuous with that of the gland above and the stalk below. 

 The inner ends articulate, at a point about half-way up the bell, with 

 shorter cells, forming the top of the bell. Both the transverse and 

 longitudinal walls of all cells are cuticularized so that when a gland has 

 been treated with sulfuric acid, these walls remain as a network (75 — 

 12) or, as it were, a cage formed of a continuous band of cuticularized 

 cell wall. In transverse section this band is T-shaped, the cross bar of 

 the T being narrow and placed towards the outside with respect to the 

 gland as a whole. Huie believed that only the outer part of the wall 

 (approximately one-half) is cuticularized, and abuts at the middle of 

 the wall on a pit connecting adjacent bell cells, the inner moiety of the 

 wall being Hgnified. Fenner did not see this, and I have been unable 

 to verify Huie's description. This parenchyma bell appears to func- 



