CONDITIONS OF THE LIFE OF PLANTS 91 



turist, and that is, the production of the quality of quality of 



the soil, 



the soil appropriate for the crop, including the in the 



necessary modification of its composition, by the the agricui- 



mechanical working of the soil ; by the irrigation or 



draining of his fields ; and lastly by the employment 



of manure. When one of the constituents of the 



soil, which, under the given circumstances, is neces- 



sary for the support of the vital functions, is absent, 



the external injurious influence is strengthened by 



this deficiency. Had this constituent been present, Effects of 



the plant would have been enabled to oppose to the senceorab- 



external hurtful influences a continued resistance, single con- 



One day may be decisive as to the life or death of 

 a plant. An accurate knowledge of the influence 

 exerted by the various constituents of the soil on 

 the diseased condition, must enable the agriculturist 

 to protect and preserve many of his fields for a long 

 time from this destruction ; but it is obvious that 

 a universal remedy against this evil does not exist. 



When the vessels of the plant are filled to over- Effects of 

 flowing with water, and the motion of the sap is 

 suppressed, the nutrition, in most plants, is arrested, 

 and death takes place. Every one knows the effect 

 of a sudden or of a gradual overfilling of certain 

 parts or organs, when the corresponding evaporation 

 is suppressed. By the endosmotic pressure of the 

 water flowing towards those cells, which contain 

 sugar, mucilage, gum, albumen, and soluble matters 

 in general, the juicy fruits and seeds approaching 

 maturity burst, and the juice of grapes, cherries, 



