28 Macfarlane— Contributions to the History of 



many of the deviation types approach the typical glands in 

 showing fusion of the radiating hair processes throughout the 

 greater part of their length. (Plate IV, Figs, ^a-^d.) Darwin 

 experimented to ascertain whether these would show aggre- 

 gation of the protoplasm, but got negative results. He insti- 

 tutes no comparison between them and the glands, however. 



The glands consist, in all cases, of two elongated basal cells, 

 with their long axes placed parallel to the course of the veins 

 (Plate IV, Fig. 7), and these are surmounted by two tiers, the 

 lowermost of two cells, the upper of a considerable number. 

 The last is covered by the surface cell layer of the gland, the 

 appearance of which has often been figured. The illustration 

 of a gland given in side view on Plate IV, Fig. 6, conveys a 

 slight idea of the beautiful intercellular protoplasmic con- 

 nections that pass through the pores in the thickened trans- 

 verse partitions of the lower cell tiers. Similar connections 

 with the surface cell layer have not as yet been traced. Gar- 

 diner has fully described the position and relation of the 

 nucleus in the surface cells before and after secretion has 

 commenced. Considerable discussion has taken place on the 

 subject of cell vacuoles and their mode of origin. Gardiner 

 states 1 that "in each cell the protoplasm closely surrounds 

 the cell-wall, leaving one large central vacuole filled with the 

 usually pink cell sap." This is true of most leaves, but it is 

 not difficult to find healthy expanded leaves whose surface 

 gland cells enclose two to five vacuoles of varying size. Such 

 leaves, however, are mostly of small size and of a green color, 

 but are irritable and secrete as usual. 



The irritable hairs are disposed in threes on each half 

 of the blade, but Errera 2 has seen four or five, and a leaf 

 that came under the writer's observation during 1891 had 

 seven on one half and six on the other, and these were 

 arranged in an irregular manner over each half. During a 

 day's hunt even for Dioncea, one often encounters leaves 

 with eight to thirteen hairs. Such facts give countenance 

 to the view that the sensitive hairs were once more numer- 



1 Proc. Roy. Soc, Vol. 36, p. 180. 



2 Bull. Soc. Roy. de Bot. de Belgique, xviii, pt. 2, p. 53- 



