Grass 
the earth affects these basal parts. The side next the 
ground grows rapidly, whilst the upper part shrinks and 
contracts. The result is to twist up the whole grass 
stem, and it becomes, if not quite upright, yet lifted up 
again, so as to be almost in its natural position. 
When fully ripe, the grains of grasses are scattered 
by some modification of the protecting bracts. 
The steppe grasses often possess a long slender awn 
which is very hygroscopic. It twists up in dry weather 
and untwists again when the atmosphere becomes moist. 
The tip of the spikelet is hard and sharp, and there are 
also short stiff hairs on its base. When such a Stipa 
fruit is lying on the ground, its long awn gets entangled 
in the grasses near it. Every twist or untwisting forces 
the point into the ground, and as the stiff hairs prevent 
its being pulled out, it is driven right below the surface. 
If it should have fallen on the back of a sheep, the result 
is often that the seed is driven right through the animal’s 
skin, and it may cause a serious wound or even death. 
It is a fact that sheep are killed in this way, indeed 
no less than four kinds of grass are guilty of sheep- 
killing. Stipa capillata commits these murders in 
Russia, and S, spartea also in North America; Aristida 
hygrometrica in Queensland, and Heteropogon contortus 
in New Caledonia have also been convicted of this crime. 
But we must turn to those grass-problems which are 
of real importance to mankind. Natural grass occurs 
under the most different conditions as regards rainfall 
and temperature, and then again there is the very 
difficult question, what is natural grass-land? There 
are, of course, many sorts of grass-land. The Phrag- 
mites thickets grow actually in water ; bank-foot colo- 
nisers like Phalaris arundinacea or Glyceria aquatica 
are also more or less under water. 
Such forms as Aira czspitosa grow just outside the 
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