ee FLOWERING PLANTS 
hairy as those of maritime grasses. The hairiness of the 
same species will vary with habitat. 
Grasses may, to some extent, indicate the presence of 
certain soils. Asa rule, they avoid chalk ; where Psamma or 
Klymus is found there is probably plenty of salt in the soil, as 
at the seaside; others indicate a sandy soil; others, again, 
the existence of much humus. 
Lastly, the various adaptations for the dispersion of the 
seeds (fruits) should be noticed. Some are so light that they 
are easily taken by the wind; in other cases the glumes serve 
as “wings.” Sometimes the stalk of the spikelet, which comes 
away with the fruit, is furnished with fine silky hairs, which 
act as an organ of dispersion, whilst those with awns are 
caught in the wool and fur of sheep and other animals, and 
are thus dispersed. The awn may develop in a variety of 
ways. Sometimes it is plume-like at its upper end and 
twisted at its base, which is more or less hard. The plume- 
like portion helps to drive it through the air, whilst the 
harder portion of the base serves to fix it in the soil (Fig. 138). 
There is no Order that is more universally distributed or 
more useful to man. Not only do some yield special articles 
of food, such as Wheat, Oats, Barley, Maize, Sugar-cane ; but 
the fact that every blade of grass all the world over is, under 
the influence of sunlight, engaged in storing up carbon and 
building up food substance, which in its turn ministers to the 
life of the animals on which man feeds, shows how important 
this Order is, from the economic point of view, to mankind. 
BIBLIOGRAPHY ON NATURAL ORDERS. 
‘‘ Handbook of Systematic Botany”: Warming, Potter. 
‘* Handbook of the British Flora”: Hooker. 
‘¢ Fertilisation of Flowers”: Miiller. 
_ ‘The Various Contrivances by which Orchids are Fertilised by In- 
sects’: Darwin. 
= aces” (Cambridge Natural Science Manuals): Ward. 
