84 A GLIMPSE OF THE LIFE OF CHLOROPHYLLOUS PLANTS. 
surpasses all. His own words in describing this are— 
“The common nettle owes its stinging property to the 
innumerable stiff and needle-like though exquisitely delicate 
hairs which cover its surface, each stinging needle tapers 
from a broad base to a slender summit, which, though 
rounded at the end, is of such microscopic fineness that it 
readily penetrates and breaks off in the skin. The whole 
hair consists of a very delicate outer case of wood, closely 
applied to the inner surface of which in a layer of semi-fluid 
matter full of innumerable granules of extreme minuteness. 
This semi-fluid lining is protoplasm, which thus constitutes 
a kind of bag full of limpid liquid, and roughly correspond- 
ing in form with the interior of the hair which it fills. 
When viewed with a sufficiently high magnifying power the 
protoplasmic layer of the nettle hair is seen to be in a 
condition of unceasing activity. Local contractions of the 
whole thickness of its substance pass slowly and gradually 
from point to point and give rise to the appearance of 
progressive waves just as the bending of successive stalks 
of corn by a breeze produces the apparent billows of a 
corn-field. But in addition to these movements, and inde- 
pendently of them, the granules are driven in relatively 
rapid streams through channels in the protoplasm which 
seem to have a considerable amount of persistence. Most 
commonly the currents in the adjacent parts of the proto- 
plasm take similar directions, and’ thus there is a general 
stream up one side of the hair and down the other. But 
this does not prevent the existence of partial currents which 
take different routes, and sometimes trains of granules may 
be seen coursing swiftly in opposite directions within a 
twenty-thousandth part of an inch of one another, while 
occasionally opposite streams come into direct collision, and 
after a longer or shorter struggle, one predominates. The 
course of these currents seem to lie in contraction of the 
protoplasm which bounds the channels in which they flow, 
but which are so minute that the best microscopes show 
only their effects and not themselves. 
