Botany and Zoology. 419 
When the leaf is held obliquely, the light is reflected as if from a mir- 
ror. The same thing occurs with drops of water thrown upon it, and 
this peculiarity can only be overcome by rubbing the leaf so as to destro 
the fine texture, by which the result is brought about. This seems to 
consist of minute capitate papille, by which a fine film of air is kept 
entangled, the water in reality never comin contact with the actual 
surface of the leaf at all—a fact established and illustrated by its reflectin 
light from its own under surface. The same phenomenon of repulsion of 
water is seen in the leaves of the Pistia stratiotes, a floating plant 
abounding in shallow tanks in India. When pressed under water the 
leaves look like frosted silver. It is the same organization that enables 
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shows the area over whi e air was emanating. The air gradually 
collected into bubbles and then rose to the surface. The quantity of air 
which rises is very great—especially from the spiral vessels when wounded 
in any way. A single stem of one-third of an inch in diameter, eontain- 
; ing tubes of a sectional area of not more than one-quarter of this, or say 
two-tenths of an inch square, even where the is cut off, has been 
airs of Urticacee.—The stinging hairs (stimuli) of Urticacese con- 
sist of a single cell, more or less elongated, swollen at its base, where it 
is sheathed by a layer of epidermal cells, and terminated sometimes by a 
sharp point, but more commonly by a small rounded pyriform or acumi- 
nated Ras This hair becomes broken in the skin, and allows the acrid 
fluid it contains to flow out. This gives rise to accidents of a more or 
less severe nature. ‘The severity of the sting depends not on the quantity 
of fluid which enters the puncture, but rather on its activity. The sheath- 
ing or bulbous portion of the hairs varies much in length. Sometimes 
it exceeds the free portion, as in Urtica feror, one of the species, which 
gives a most dangerous sting. In some species of Urera. oh in one or 
two other genera, the sheathing portion increases much wi age, aro ate 
Woody, and forms a true prickle or aculeus, analogous to those 
ose and of so ies of Hibiscus. - ; 
Glandular hairs, properly so called, are rare among —_—— 
recies of Fleury present examples of these hairs, as - as - ‘ 
= the lower surface of Parietaria communis, on which we also notice, as in 
_ Forskohlea and some other genera, hooked or uncinate hairs. 
