STROXO DB.INK AND TOBACCO SMOKE. 65 



burdock and dock (plants growing wikl nearly every- 

 wkere in Britain, and to be had for the plucking), 

 or either of tliese, again, with comfrey ; and all three 

 with the tobacco leaf. Observe the forms of their 

 bases, points, and margins, and. the characteristic dis- 

 tinctions of them will be immediately apparent. 



Take a portion of the midrib of each leaf, and cut a 

 very thin slice of it at a right angle to its length, and 

 compare them with each other under the microscope 

 with an object glass of low power. The differences 

 of these will be seen in the general forms of their 

 outlines, whether plain, grooved, or lobed, and the shape 

 and distribution of the ivoody amongst the cellular 

 tissues. Notice, more especially, the general outlines 

 and upper surfaces of the midrib sections of dock (Plate 

 9, fig. 11), and burdock (Plate 9, fig. 8), and the marked 

 characters which distinguish them from that of tobacco 

 (Plate 9, fig. 5) or comfrey (Plate 10, fig. 5). Those 

 of cliicorij (Plate 10, fig. 2) and foxglove are as de- 

 cidedly marked. 



Carrying our analyses still further, by adding greater 

 power to the microscope, our leaves furnish us with 

 invaluable and infalliljle evidence in the minute hairs 

 with which their surfaces are clothed, and which, from 

 their delicacy and pliability, elude the grinding action of 

 the snuff'-mill. These hairs are attached to, and grow 

 on the skins of the upper and under surfaces of leaves, 

 their micMbs and veins, lying scattered in greater or 

 less a.l)undance amongst the stomates or breathing-pores 



F 



