MULCHING, SHADING, AND WATERING. 143 



none on dryer soils. The constant dampness of the atmos- 

 phere, produced by excess of water in the soil, diminishes 

 evaporation from the leaves of plants, and hence renders 

 the process of assimilation slower, and less food is taken 

 up by the roots. By diminishing the absorption of car- 

 bonic acid, it lessens the atmospheric supply of food. It 

 creates a tendency in the organs of plants to vary from 

 the normal type of growth, changing the flowers, for in- 

 stance, into green leaves and ill-formed shoots. 



Succulent plants, those with fleshy roots, and those with 

 leaves that appear dry, and transpire but little, and in 

 which vegetation proceeds slowly, are most subject to in- 

 jury from excess of water. Plants growing in a clear light 

 are less endangered by an over supply, than if growing in 

 a shaded situation, as they can both assimilate and perspire 

 more. Plants in pots are most likely to be injured by in- 

 judicious watering, at times being drenched with too 

 much, and at others allowed to become too dry. 



Where water exists in excess, it must be removed by 

 drainage. This is indispensable in pot culture. It is par- 

 ticularly to be attended to in the case of plants which are 

 to be kept through the winter in green-houses or pits. 



The quantity of water that plants require varies with the 

 species of plant and with its condition, whether in a state 

 of growth or repose. A plant cultivated for its leaves re- 

 quires more water than if grown for its flowers, and still 

 less is needed if grown for its seeds or fruit. In propor- 

 tion, also, as the roots of plants extend into the earth, the 

 less water at the surface is required. Tap-rooted plants, 

 like cotton, when once established, are not apt to suffer 

 from drought ; but those with roots at the surface only, 

 need frequent watering. Perennial plants, also, in general 

 require less the artificial application of water than annuals. 

 The growth of the former is merely suspended by dry 

 weather for the time being, to be resumed when moisture 

 is supplied ; but if water and the food of which it is the 



