EPIDERMIS, 



89 



secretion appears in the walls between neighbouring cells : these may be called 

 glands with intramural secretion, or shortly ifitra??iural glands. Besides those which 

 result directly from the presence of the secretion there are in most, but not in all 

 cases, other peculiarities of form and structure connected with glandular cells. 



{a) Bladder-like dermal glands. The peculiarity of structure of the bladder-like 

 glands consists in the appearance of the secreted body at the limiting surface 

 between cuticle and cell-membrane. While the form and turgescence of the cell 

 remain the same, the secretion, as it increases in quantity, raises up the cuticle like a 

 bladder : either the cuticle grows simultaneously, while its thickness remains the 

 same or increases, or its surface growth does not keep pace with the increase of 

 the secretion, and hence it becomes strongly stretched, and at last is easily burst. 

 The stickiness of the surface arises from the fluid secretion thus set free by the 

 bursting of the cuticle. The rent cuticle, according to Hanstein, may be repeatedly 

 renewed on young parts. 



These phenomena are best seen in the glandular hairs. According to their 

 external development these belong for the most part to the capitate form, and the 



Fig. 31. 



FIG. 32 



Fig. 33- 



Fig. 34. 



Figs. 31— 34.— Glandular hairs of the petiole of Primula sinensis. Fig 31 (142). In n the secretion beginning. *, with a large 

 secretory bladder ; d an old hair, the bladder has burst and the upper part disappeared.— Figs. 32—34 (375) Fig. 32= a of 

 Fig. 31. a' with intact secretory bladder lying in water ; a" after solution of the secretion in alcohol. Fig. 33. c end of hair, 

 intact ; c' the same after solution of the secretion by alcohol. Fig. 34 = (f of Fig. 31 under higher power. 



position of the glandular structure and secretion is at the head. When the latter 

 is the expanded head of a unicellular hair, e. g. on the leaf of Aspidium molle S 

 or the terminal cell of a compound hair, e. g. leaves of Primula sinensis (Figs. 31 to 

 34), Pelargonium zonale, Pogostemon Patschouli, &c., its membrane is equally thick 

 all round, delicate and surrounded by the cuticle which is also thin. At the apex 

 there then begins a thickening of the wall which gradually increases in strength 

 and in extent from the apex backwards, spreading over the apical half of the 

 head (Primula sinensis), or even further backwards, and attaining in the Ferns 

 above-named the strength of a firm cell-wall, and in Primula and Pelargonium the 

 bulk of a thick cap, which even exceeds the apical cell in size. The thickening of 

 the wall consists from the first of the resinous body, which, as shown when burst, 



* Also the teeth of the Palece of Aspidium filix mas, and, as an exquisite example, the glandular 

 hairs which occur in this and allied species in the intercellular spaces of the Rhizome." 



