113 



stance. In agricultural crops the amounts of water are still larger, 

 sometimes reaching 95 per cent of the whole weight. 



The amounts transpired by cereals, grasses, weeds, etc., are consid- 

 erably larger than the preceding, as shown by the following table 

 compiled from AVollny's results,: 



The following table is given by Risler (1873) in his " Note on the 

 diminution of the volume of water courses," and shows the mean daily 

 consumption of Avater by plants, expressed in millimeters of depth 

 of water over the area of the field : 



These numbers have been deduced from the results of many years of 

 experiments in the laboratory and from observations made in a 

 drained field under conditions favorable to this kind of research. 

 The crops have necessarily varied from one year to another, but 

 unfortunately I am not acquainted Avith these details. 



The transpiration of the plant is only a means to an end. (See 

 Marie-Davy, 1875, p. 209.) Its object is the introduction into the 

 vegetable organism of the mineral elements necessary for the develop- 

 ment of its tissues and that of the other principles united there. 

 The experiments of Woodward and those of Lawes have already 

 shown us that the same quantity of water is not always necessary 

 in order to furnish the same amount of mineral substance and to 

 produce in the plant all the elaboration and movements of organic 

 products which should be produced there. 



It appears evident that in soils more or less fertile and which con- 

 2667—0.5 M 8 



