32 Macfarlane. — Contributions to the History of 



of removing the hairs do not aid us here, as he does not 

 state whether the leaf that had opened after removal of all 

 the hairs was still irritable in the areas from which they had 

 been removed. But even were such true — and Balfour's ex- 

 periments favor it — it is still possible that minute drops of 

 liquid might escape through pore apertures in the cut cell 

 walls, just as we suppose that these escape from the pores on 

 the unthickened areas. 



The lower part of the shaft consists of three tiers of shal- 

 low, closely-packed, cells, succeeded by another tier, the cells 

 of which are more elongated and have their upper septa 

 more or less obliquely placed, and wedged in with the lower 

 ends of the shaft cells above. The terminal shaft cells are 

 elongated, thick-walled, and taper into each other. Their 

 walls are traversed by numerous pore canals, and their cavi- 

 ties are filled with finely granular protoplasm, but we have not 

 succeeded in tracing intercellular connecting threads. The 

 internal or central cells of the shaft greatly resemble those of 

 the epidermis in size, shape, and structure. 



The epidermal cells of the upper leaf surface are elongated 

 and nearly quadrangular in outline, and are covered by a thick 

 cuticle that is in proportion to the cuticle of the lower leaf 

 surface as 3 : 2. 



Of all the plants examined by the author for intercellular 

 protoplasmic connections Dion&a yields the finest results in 

 its epidermal cells. Such are best attained, however, by a 

 modification of the ordinary mode of treatment that was grad- 

 ually arrived at during the course of the present inquiry, and 

 is described in the footnote. 1 One readily notices then (Plate 

 IV, Fig. 8) along each side wall eighteen to thirty proto- 

 plasmic bridges which are slightly constricted on either 

 side of the cellulose wall, and form a central swelling at 



1 The following has been found invariably to give better results than the methods rec- 

 ommended by Gardiner, Keinitz-Gerloff, and others. After iodine treatment the fresh 

 sections are placed in twenty-five per cent, sulphuric acid, and left for one to two hours. 

 They are then removed thrown into water, thoroughly washed in changes of it, and there- 

 after stained in a strong solution of watery eosin for at least an hour. Rapid washing 

 in water then removes the stain from the swollen walls, and brings out sharply the cell 

 protoplasm and threads of a rich crimson-red color. These show very clearly if mounted 

 in a cell with two per cent, glacial acetic solution which fixes the stain. 



