32 VEGETABLE ORGANS. 



the epidermis covers not only the leaves, but every 

 part of the plant. 



Hairs. Arising from the epidermis are the hairs 

 of plants. These are thread-like or filamentous pro- 

 longations of the epidermis beyond the surface of the 

 leaf (PI. I. fig. 12), consisting of cells arranged end 

 to end. They are often branched, sometimes star- 

 shaped (stellate) (fig. 28), and present great varieties 

 in form, as shown in the figures, the plants from 

 which these were drawn being mentioned in the De- 

 scription of the Plates. Sometimes hairs terminate in 

 a little head (PL I. figs. 12 c, d, e\ the cell or cells 

 composing which secrete a colouring or a viscid sub- 

 stance ; they are then termed glandular. The hairs 

 of plants are particularly interesting to the micro- 

 scopic observer, not only on account of their curious 

 forms, but in connexion with the remarkable pheno- 

 menon of the circulation of the cell-contents, or 

 rotation, as it is called, observable in them. This is 

 difficult to be perceived by any one unaccustomed to 

 microscopic observation, because the particles by 

 which the motion of the cell-contents becomes evi- 

 dent are exceedingly minute ; but practice in the use 

 of a high power will overcome this difficulty. The 

 hairs which exhibit the phenomenon best are those of 

 the American Spiderwort (Tradescan'tia Virgin' ica\ 

 which is to be found in every garden. It may, per- 

 haps be recognized thus : The plant is about a foot 

 and a half high; the leaves are sword-shaped and 

 channelled, and the flowers are purple, in heads, and 

 \\ inch in diameter. The hairs are attached to the 

 sides of the stamens, towards the lower part or base. 

 The stamens should be carefully picked off with for- 

 ceps, and placed on a slide in a drop of water ; the 

 hairs should then be separated with the mounted 

 needles, and a cover applied. Under a low power, 

 the hairs are seen to be beaded or momTiform (momle, 

 a necklace), and of a fine purple colour (PL I. fig. 22). 



