APPENDAGES OF THE EPIDERMIS.——HAIRS OR TRICHOMES. 63 
Upper surface Lower surface 
Be) ye 2 gs 25,000 20,000 
Wucea,. . ; . 40,000 40,000 
Clove Pink . - 98,500 38,500 
Stomata are not found upon all plants. Thus they are 
absent from all Thallophytes, but in the higher orders of Cor- 
mopbytes, as the Ferns and their allies,,they abound, while in 
the Liverworts and Mosses they are confined to certain parts. 
They exist more or less upon all Flowering Plants and their 
organs. But they are far more abundant upon those organs 
which are green ; thus they are found especially upon leaves, as 
we have seen, but more particularly on their under surface. 
On the floating leaves of water plants, as in the Water-lily, how- 
ever, we find them only on the upper surface ; while in vertical 
leaves the stomata are equally distributed on the two surfaces. 
They occur also on the young green stem and branches of plants ; 
and on the parts of the flower. In those plants which have no 
foliage leaves, as the Cactacex, they abound upon the green 
succulent stems. They are commonly only found on those parts 
which are furnished with a true epidermis, and are accordingly 
absent, as a rule, from roots and all submersed parts of plants. 
Sachs and others have pointed out that there is a connexion be- 
tween the distribution of stomata on leaves and their protection 
from wet by the wax-like coating commonly known as ‘ bloom;’ 
and recently this has formed the subject of an interesting series 
of investigations by Francis Darwin (see Journ. Linn. Soc. 
(Bot.), vol. xxii. p. 99). 
5. APPENDAGES OF THE EpimpERMIS.—Upon the surface of 
the epidermis, or in the sub-epidermal tissue, there are fre- 
quently to be found certain structures consisting of one or more 
cells of different forms, variously combined, and containing 
various substances. These are termed, collectively, Appendages 
of the Epidermis; and, as their name implies, they have no 
connexion with the fibro-vascular tissue of the leaves, branches, 
or stem. We shall treat of them under the two heads of Hairs 
and Glands ; although in many cases we can draw no distinct 
line of demarcation between these structures. ; 
(1.) Hairs or Trichomes.—These are thread-like prolonga- 
tions externally of the epidermal cells covered by cuticle (jigs. 
123, g, g, and 129). They may either consist of a single cell, 
when they are called simple hairs (figs. 137-141), or of several 
cells, when they are termed compound (figs. 144 and 145). 
Simple hairs may be undivided (jig. 137), or forked (fig. 138), 
or branched (jig. 139). A beautiful form of simple hair is 
that called stellate, as seen in Deutzia scabra, Alyssum, &c. 
(figs. 140 and 141) ; this is formed by a cell dividing horizontally 
into a number of parts which are arranged in a star-like form. 
Compound hairs may be also undivided, as is more frequently 
