66 STRONG BRINE AND TOBACCO SMOKE. 



of these parts. The tobacco leaf is furnished with 

 two forms of hairs, long and short. The former are 

 composed of three or four elongated cells, joined end to 

 end, the whole surmounted by a cluster of minute cells, 

 forming a gland which contains a rich brown colouring 

 matter. These are called glandular hairs, and they 

 have a pair, sometimes more, cells forming a compound 

 base. The short hairs are unicellular, with a cluster of 

 cells at one end, also containinoj colourins^ matter. I 

 call these hairs club-shaj^ed ; their bases are simple 

 (Plate 9, figs. 2, 3, 4). 



The leaves of dock are furnished with peculiar club- 

 shaped unicellular hairs, free from colouring matter, 

 but having their surfaces marked with peculiar wavy 

 lines (striated), formed by a wrinkling, as it were, of 

 thin cell walls (Plate 9, fig. 10). This is a very marked 

 feature of them ; equally so is the presence on the skin of 

 the blade, or thin portion of the leaf, of numerous circular 

 cavities (glands), composed of clusters of cells built into 

 the substance of the leaf, forming minute chambers con- 

 taining crystals of oxalate of lime (raphides) (Plate 9, 

 fig. 12). The hairs described are found mostly on the 

 midribs and veins of the leaves, the glands on the 

 leaf-blades. 



Leaves of the hiirdock plant are covered on their 

 under surfaces with a dense, greenish- white, woolly 

 substance. AVhen a minute portion of the skin to which 

 this is attached is separated from the leaf, this woolliness 

 is resolved by the microscope into a mass of very beau- 



