THE SHADING OF PLANTS 



121 



"T%T"N*, 



Fig. 174. Raising tea under shelter in South Carolina. 



essential to nitrogen assimilation. Just what in- 

 tensity of light may be the optimum for this par- 

 ticular function is not known, and there are doubt- 

 less complex relations to be considered. At any 

 rate, the proteid content 

 is usually less in shaded 

 plants. 



(6) It has been held 

 that there is an increase 

 in the acid content of 

 shaded plants. This may 

 be relative. A certain 

 amount of acid lends 

 quality and flavor, while 

 an increase without gain 

 in sugar may be deci- 

 dedly objectionable. In 

 shading strawberries 

 with cheese-cloth it has 

 been shown that there is 



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^**-*Af&4Srate*g*. r '.-..ftH^BjjfU. 



Fig. 175. Muslin-covered plant house 

 Experiment Station, 



will develop normal flowers or fruit, even 

 when grown from bulbs or other storage 

 organs, and a general effect of etiolation is 

 usually apparent in the reduction of fruit- 

 ing, while increased or continuous illumina- 

 tion often hastens flowering or fruitage, or 

 may lengthen the flowering period. How- 

 ever, when there is only partial shading it 

 is quite possible that the size of succulent 

 fruits may be increased, and the time of 

 ripening hastened, for the moisture and 

 temperature factors under half-shade will 

 play important roles. It has been found, 

 for instance, that under cheese-cloth sev- 

 eral varieties of strawberries bear a larger 

 fruit ; and that lettuce runs earlier to seed, 

 (b) Indirect effect through the environment. 

 — The practice of shading may modify the 

 factors of the environment in a variety of 

 ways ; and each of these factors is impor- 

 . tant in the life relations of the plant. The 

 purpose, of course, is primarily the modified light 

 effect, yet frequently the effect on other factors is 

 much more important. Aside from reducing the 

 light, shading is important in the relations of the 

 plant in order 



(1) To regulate hu- 

 midity. 



(2) To conserve soil 

 water. 



(3) To mitigate or 

 equalize temper- 

 ature. 



(4) To give partial 

 protection from 

 wind. 



(5) To maintain bet- 

 ter physical con- 

 Hawaii dition of the soil. 



an actual reduction in the acid content. The acid- 

 ity, however, is more marked in taste, and this be- 

 cause of a marked reduction of sugar. The reduc- 

 tion of the sugar content, as well as of certain 

 other carbohydrates in fruits, seems to be general 

 under such cultural conditions. 



(7) The aromatic products may not be 

 very important as animal nutrients, but 

 they are physiologically essential, and 

 represent almost the sole value of eco- 

 nomic plants used as condiments. In 

 1838, De Candolle called attention to 

 the diminished production of savors and 

 odors in shaded plants. It was found 

 later that plants removed from south- 

 ern latitudes to the latitude of Scandi- 

 navia during the two months of maxi- 

 mum sunshine in the latter region, 

 showed an increase in the development 

 of aromatic products. Indeed, it has long 

 been suggested that many fruit-bearing 

 plants containing objectionable flavors 

 might be benefited by etiolation. 



® In total darkness very few plants 



(1) In wet periods, 

 shaded plants may have no advantages, certainly 

 none so far as the humidity is concerned ; but in 

 dry weather the humidity is reported as more reg- 

 ular under partial shade. This relation is important 

 in dry regions. It is a mistake to assume that 



Interior construction of house shown in Fig. 



