Chapter X —123— Drosera 



The emplacement of the glandular tissues is different in the marginal 

 tentacles. Here the end of the tentacle stalk is formed into a spoon, 

 in the bowl of which lies the gland. There is, as it were, a torsion of 

 the upper part of the tentacle so as to bring the gland on the upper 

 ventral surface. The complete homology of the two types is seen on 

 examination of a transverse section of the marginal gland {13 — 9, n; 



zd — I, 2). 



To be included as a specialized portion of the gland, or better a 

 portion of the tentacle acting in a specialized way in cooperation with 

 the gland, is, according to Fenner (1904), the uppermost course of 

 epidermal cells of the stalk, those, namely, which are in direct contact 

 with the tissues of the gland at its base. These cells are short and 

 being epidermal, they form a circle of 8-10 cells called by Fenner the 

 "Halskranz", or as we may call them, the neck cells. Sometimes 

 there are two rows of neck cells (Konopka), and this I note may be 

 the case in D. Whittakeri. The neck cells surround the parenchyma 

 cells of the same transverse course but these latter are not included in 

 the "Halskranz", as defined by Fenner, who describes the anatomi- 

 cal relations as follows. The neck cells are in contact above with the 

 lower ends of the emergent parenchyma bell cells, and with the outer 

 zone of the xylem mass of the gland. Inwardly they lie in contact 

 with the short parenchyma cells of the stalk, these in turn lying against 

 the inner zone of xylem tracheids and with the end of the stalk vascu- 

 lar bundle. Below, the neck cells impinge on the stalk epidermis. 

 They are, as one may say, in a strategic position to carry on a special 

 function, if Fenner is right in his interpretation. That they have a 

 function he beheves is evidenced by the presence of numerous pits in 

 their walls which He against the parenchyma bell cells and those of the 

 xylem, and furthermore, by the fact that their cuticle is porous. He 

 gives the following interpretation. The neck cells receive water from 

 the bell cells which bring water from the upper part of the xylem mass, 

 and from the lower xylem cells, presumably also from the parenchyma 

 transversely within the neck cells, and pass it outwardly through the 

 pores of the cuticle supplying fluid to dilute the viscid mucilage se- 

 creted by the glandular cells above. The glistening drop of mucilage 

 supported on the tentacle head is, says Fenner, pear-shaped, the 

 broad part of the drop being around the neck cells because the fluid 

 exudes chiefly from them. The reasoning here appears disingenuous. 

 Nor is his statement that the cuticle is porous acceptable since dyes 

 (methylene blue) never enter the outer surface of the neck cells, but 

 pass into the stalk only by diffusion through the gland, as I have 

 verified repeatedly. While crediting Fenner with imagination, it is 

 still permitted to doubt the correctness of his interpretation and even 

 the supposed facts on which it is based. Konopka indeed has taken 

 issue with Fenner, and his view is stated beyond. 



The development of the tentacle has been worked out by Homes, 

 and it becomes evident that the outermost layer of the gland is purely 

 epidermic in origin, as would appear on the face of it. The second 

 layer, which might be interpreted as of epidermic origin, is shown to 

 be of parenchymatous origin. The third layer, the parenchyma bell, 

 is partly epidermic and partly parenchymatous (Fenner). Those 



