THE WATER REQUIREMENTS OF FRUIT PLANTS 



11 



requirements of plants by increasing both the moisture content of the soil 

 and the supply of available plant nutrients. 



Light. — It should not be inferred from what has been said, that the 

 plant's water requirement is entirely governed by its nutrition. Investi- 

 gation has shown, for instance, that in tobacco, the amount of water 

 absorbed is quite independent of the amount of mineral constituents 

 taken in.** Thus the average ratio of water to ash for six plants grown 

 in the open was 2,548, while for six plants grown under shade it was 1,718. 

 These data, however, apply only to the water-ash ratio of plants growing 

 in full sunlight and in shade. For the water-dry-matter ratio in sunlight 

 and shade a somewhat different condition holds, probably because of the 

 influence of the sunlight in promoting photosynthetic activities and the 

 storage of elaborated materials. 



Table 10. — Water Requirements per Unit of Dry Weight of Leaves in Sun and 



Shade 



{After HoneP^) 



(Kilograms per 100 grams of dry leaves) 



Species 



Sun 



Shade 



Beech \ 76 . 18 



Hornbeam ; 81 . 30 



Sycamore 61 . 69 



Scots pine 19. 15 



Silver fir 13.91 



Black pine 8 . 76 



107.80 



98.90 



76.19 



5.02 



4.85 

 5.25 



Data presented in Table 10 show that in all the broad-leaved trees 

 studied, the water-dry-matter ratio rose in the shade, though with the 

 conifers it was greatly lowered. The data on tobacco alone might 

 suggest that with the nutrition factor constant more water would be 

 required in exposed than in protected situations and that shading and 

 windbreaks might be expected to reduce materially the plant's water 

 requirements. On the other hand, the data of Hasselbring and Honel 

 together lead to the inference that though the mineral requirements of the 

 plant as related to water suppl}^ may be increased in exposed and de- 

 creased in protected situations, tissue building and the manufacture 

 and storage of elaborated materials may be promoted by the opposite 

 conditions. 



In General. — Recent investigations by Briggs and Shantz^^ iead 

 them to conclude that when a crop is thoroughly adapted to a certain 

 environment it has its water requirement at the minimum and that its 

 water requirement gradually increases as it is forced to grow in more 

 and more uncongenial conditions, whatever they may be. Thus as a 



