392 
SOME GENERAL PLANT PROBLEMS 
grow with much less moisture than the ordinary strains 
demand. The use of such strains makes crops possible on 
land too dry for farming under ordinary conditions. 
The use of water for irrigation has been practiced from very 
early times especially in India and Egypt. The methods 
used there, and the results obtained, however, are insignifi¬ 
cant when compared with modern methods, a good example 
of which we find in the western United States. Immense 
dams are constructed which impound lakes covering many 
Figure 359. — Irrigating' Ditches. 
acres. The water from these lakes is let out, carried miles 
through canals and tunnels, and is distributed to crops 
as needed. In this way, nearly a million of acres have 
already been made fertile which before were unable to produce 
crops on account of the absence of rainfall. 
This work in the United States is carried on by the govern¬ 
ment under the name of reclamation 'projects. More than 
twenty such projects have been successfully carried out, 
and the land sold to settlers at reasonable rates. More 
than twenty thousand persons are now living in regions 
formerly unfit for habitation. It is estimated that there 
