THE ITHEOKY OF WATEEING . 207 



the native country are unknown to us, the external appear- 

 ance of the plant may give us some clue to its proper treat- 

 ment. Plants with narrow and tough leaves, especially when 

 the leaf-blade is vertically placed, do not, « as a rule, like 

 much water ; plants with broad leathery leaves prefer a damp 

 atmosphere to great moisture of the roots. Succulent plants 

 with hard epidermal cells (leafless Euphorbias, succulent Com- 

 posites, Aloes, and Agaves), and thin-leaved plants with a 

 strong woolly covering of hairs, are further examples of plants 

 which require little water. 



Then the structure of the roots may often reveal the re- 

 quirements of the plants. Succulent roots in the case of 

 thin-leaved plants, and less succulent ones which taper away 

 and grow rapidly to the bottom of the pot, usually like, and 

 often require, a large amount of water. On the other hand, 

 a multiplicity of fine branching rootlets which tend to grow 

 out above the surface of the soil can often do with a small 

 amount of water, but require a greater amount of aeration. 



In watering we must attend quite as much to this desire of 

 the roots for air as to that for water. 



As we have already had occasion to mention, the roots 

 require just as much as the stem structures a thorough supply 

 of air. If this is not forthcoming, alcohol is formed in the 

 cortical tissue of the root, and later on fusel oil and acids 

 (acetic acid, butyric acid, &c.) make their appearance, and 

 these acting poisonously, generally cause the death of the 

 organ. The products of decay are then transported from 

 these dead portions of the plant to the still living organs, and 

 the inevitable result is the death of the latter. 



The most frequent cause of the formation of alcohol in 

 roots and the subsequent decay of the latter is a permanently 

 wet ball of roots. The unfounded fear of damage arising 

 from a lack of water causes gardeners to water the pots as 

 soon as the surface of the soil begins to dry ; and it is not 

 taken into consideration that the centre of the pot still con- 

 tains a large amount of water. The consequence is that the 

 lower part of the pot is continuously saturated with moisture. 

 Thus the air is prevented from passing freely to the roots, and 

 these are gradually suffocated. This suffocation of plants 



