Dioncca Muscipula, Ellis. 29 



mis and diffuse in distribution, a condition still retained 

 by Drosera. 



Each hair is an emergency, and consists of three well- 

 marked regions, the base, the joint and the shaft. 1 The hair 

 base consists externally of four to five tiers of epidermal cells 

 that gradually rise up from the leaf blade. Each tier is a cyl- 

 inder of eighteen to twenty-two cells with thickened walls that 

 are traversed by intercellular threads of protoplasm. These 

 enclose loose and slightly elongated cells with rather thick, 

 clear walls, the cells being continuous with those of the meso- 

 phyll. ( Plate IV, Fig. 3.) The protoplasmic masses of all of 

 these are connected by threads with each other, and with 

 those of the mesophyll cells. The joint or special irritable 

 centre is remarkable. It is a cylinder of elongated quadrangu- 

 lar epidermal cells, each three and a half to four times longer 

 than broad. These enclose a central cylinder of mesophyll 

 cells that are similarly elongated. In all hairs yet examined 

 — and this applies to twenty-three— the cuticle that is strongly 

 developed over the general epidermis gradually thins out over 

 the basal cells, and is either quite absent over the irritable 

 joint cells or so very delicate as to escape detection when 

 acted upon by cuticular tests. The middle part of each epi- 

 dermal joint cell is, in all hairs yet examined, creased or puck- 

 ered upon itself, so that it at first gives the impression of trans- 

 verse dividing walls on surface view. (Plate IV, Fig. 1.) These 

 creasings have evidently misled observers into giving imper- 

 fect views of the hairs. The question naturally arises whether 

 these exist in the unstimulated hair or are due to collapse of 

 the cells, which, up to period of stimulation, are turgid. One 

 would regard the latter as the more likely view, but so far as 

 we have been able to bring the microscope to bear on open 

 leaves, the joint cells appear always to be puckered. But a 

 structural feature of some interest is the presence over the 

 free face of each cell of minute pits which seem exactly to 

 agree with those noticed by Gardiner* on the terminal hair 



1 We are unable to agree with Goebel (Bot. Schild. ii, 1891), in dividing the hair into two 

 parts, since the relation, structure and behavior of the three areas that we have indicated 

 prove them to be distinct alike in structure and function. 



« Proc. Roy. Soc, Vol. XXXIX, p. 229. 



