244 GARDENING FOB THE SOUTH. 



and its capacity for heat diminishes. The constant evapo- 

 ration from wet soil so lowers the temperature of the 

 adjacent stratum of air, that frosts occur when there are 

 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. Jt 

 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 injury from excess of water. Plants growing in a clear 

 light are less endangered by an over supply than if grow- 

 ing in a shaded situation, as they can both assimilate and 

 perspire more. Plants in pots are most likely to be in- 

 jured by injudicious 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 requires more water than if grown for its flowers, 

 and still less is needed if grown for its seeds or fruit. In 

 proportion, 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, 



