152 
POPULAR SCIENCE REVIEW. 
usual way with the polariscope, lit up with rich colours ; or they 
may be viewed with ordinary light, either as opaque or trans- 
parent objects. Each hair is simple, something like that of 
the cabbage, but a considerable number grow out from a com- 
mon base, forming radiating tufts. 
Having considered hairs in simple and compound forms, as 
soft structures and as hardened into thorns, the transitions 
from hairs to scales should be observed; and many ferns will 
supply good illustrations. The hairs on the stems of the 
large parti-coloured-leaved Begonias are thickly furnished with 
hairs, composed of a multitude of cells, looking somewhat like 
scales to the naked eye, but under the microscope they exhibit 
a complicated cell-structure, and show how easy it is to pass 
from simple hairs to higher forms. 
Many hairs are glandular ; that is, they act like glands, and 
secrete some peculiar material. The best known is that of the 
stinging-nettle, providing the acrid poison that escapes as soon 
as a slight touch breaks off the brittle point. Hairs that 
secrete and store up remarkable colouring matters will be 
readily found by examining plants on the roadside or in the 
garden. A common St. John’s Wort {HyjpeHcum pulchrum) 
has its leaves furnished with a fringe of club-shaped glands, 
similar in structure to many stumpy hairs, and filled with dark 
pigment (Fig. 4.) Interesting hairs with glandular tips will 
be found on the sepals of the American Currant {Rihes san- 
guineosum), common as an ornamental shrub. 
The surface glands of leaves are essentially the same in con- 
struction as hairs, being expansions of the cuticle. They differ 
from the deeper glands (internal glands) below the cuticle, 
which can be well seen in a vertical section of orange-peel. The 
ornamental Coleus plants, common in every conservatory, 
afford interesting specimens of surface or cuticular glands. 
The under surface of the leaves should be examined as opaque 
objects with powers of from 60 to 100 or more, and numerous 
little balls, slightly indented with a cross, will be seen to shine 
like topaz gems. They may be found well developed in very 
young leaves ; and such leaves, if also adorned with numerous 
hairs, filled with purple and white fluids, make splendid objects 
when well lit up. The little glands contain a fluid that seems 
to pass into a resinous state, changing to a redder tint when 
simply dried. A leaf flattened and dried in a book, then 
placed on a slide covered with thin glass, with paper pasted 
round the edges, or the edges cemented with varnish, keeps its 
colour sufficiently well to be worth preserving. In a specimen 
before the writer at this moment, put up a year ago, the 
glandular balls have retained their form and size very closely, 
changing to a darker tint, and the hairs with which the leaf is 
