RESPONSE OF FRUIT PLANTS TO CONDITIONS OF SOIL 



79 



Table 37. — The Influence of Moist and Dry Soil and Air on Size of Leaf 

 OF Tropaeoltjm Majus 



_ (After Kohl^^) 



results are to be found in aquatic plants on the one hand and in desert 

 plants on the other. In the former the cuticle is usually thin and per- 

 meable, the stomata are numerous and exposed, frequently the surface 

 of the epidermis is enlarged and woody tissue, sclerenchyma and col- 

 lenchyma are poorly developed. In xerophytic plants, growing under 

 very dry conditions, the cuticle is thickened and rendered imperme- 

 able by waxy impregnations; the surface of the entire plant is reduced to a 

 minimum, the stomata are few in number and frequently situated at the 

 base of depressions in the surface of the leaf. Wood and fibers are 

 developed to a marked degree and specially differentiated water storage 

 tissue is of frequent occurrence. 



Apparently atmospheric humidity, rather than soil moisture, soil, or tempera- 

 ture, is the factor determining the limits for the production of certain 

 varieties of dates. Those of the Deglet Noor type thrive only in the driest 

 cUmates, Hke that of the desert oasis with a mean humidity of 35 to 40 per cent. 

 Dates of a different type are grown in the vicinity of Alexandria, Egypt, with a 

 mean annual humidity of 68 per cent.*^ 



Russeting of Fruit. — In addition to the more general influences of 

 atmospheric humidity and soil moisture on plant development there 

 are certain more or less specific influences on fruits and fruit plants. 

 One of the most conspicuous and frequently observed is the effect on the 

 russeting of the skin of certain pomaceous fruits, particularly the apple 

 and the pear. This results from a cracking and weathering off of the 

 epidermis and an increased development of the corky parenchyma 

 beneath. It occm-s especially in humid climates or during rainj^ sea- 

 sons. For instance the Bosc and Winter Nelis pears as grown in the dry 

 atmosphere of the Rogue River valley of southern Oregon are practi- 

 cally smooth skinned fruits. Grown in the more humid Willamette 

 valley a hundred miles farther north their surface is almost completely 

 russeted. The Cox Orange apple is a half russet variety as grown in 

 England; it is a smooth-skinned fruit as grown in the Okanogan region in 

 British Columbia. The fruit trade generally considers that fruit pro- 

 duced in irrigated sections has a higher "finish" than fruit of the same 



