10 SHADE IN COFFEE CULTURE. 



scarcely be based on the Angolan natural conditions. But whatever 

 the natural limits of the genuine species or variety, the fact that it 

 has been found generally possible to grow it to maturity at sea level 

 in moist tropical countries is an indication, from the vegetative stand- 

 point, that the disadvantages suffered at low elevations are not neces- 

 sarily serious, and there are also reasons for supposing that they may 

 result from too much heat, too much dryness, or, in other cases, too 

 much moisture. It would, in fact, be more logical to reverse the 

 argument noticed above and to suggest that the Arabian coffee may 

 suffer at low altitudes for lack of the powerful insolation 1 under which 

 it reaches perfection in mountain districts. 



The fact that coffee is sensitive to drought requires that for increased 

 temperature the available moisture must also be increased and sus 

 tained. The difficulty with coffee at low altitudes when this require- 

 ment is met is not a failure to grow; on the contrary, the vegetative 

 activity is too vigorous for practical results. Instead of flowering at 

 a definite time, a succession of blossoms is put forth; the berries also 

 ripen irregularly and often are not properly matured. The cost of 

 culture and harvesting are increased and the quality of the product is 

 inferior. 



EFFECT OF SHADE ON YIELD. 



The fact that shade by lowering the temperature and increasing the 

 humidity may render it possible to produce coffee in regions so hot 

 and so dry that none could be grown otherwise, has little bearing on 

 the problem of ascertaining the value of shade in rational culture 

 under conditions naturally favorable to the coffee plant. While there 

 have been no scientifically conducted experiments to test the effect of 

 shade upon yield, every consideration of vegetable physiology agrees 

 with the frequent admission of planters that shade decreases the yield, 

 especially where it assists in retaining excessive moisture either in the 

 air or in the soil. That sunlight is necessary for the processes of 

 plant assimilation, that the sugar content of vegetable tissues depends 

 upon access to light, and that sugar is the material from which most 

 of the alkaloids and other plant substances are elaborated, are well-' 

 known facts indicating the necessity of light for a maximum of func- 

 tional activity. Even those who advocate the use of shade admit, as 

 in Porto Rico, that the yield is diminished, though the existence of 

 compensating advantages is maintained. It is true that in Porto Rico 



^n connection with physiological and ecological studies of plants the word "inso- 

 lation" means exposure to the radiant energy of the entire solar spectrum, and is 

 also employed conversely in referring to the direct results of such exposure. In 

 different sciences the energy radiated from the sun is considered with reference to its 

 optical, thermal, actinic, electric, or other qualities, but in dealing with plants "inso- 

 lation" involves possible effects from all parts of the spectrum, conditioned only by 

 the properties of the intervening atmosphere. 



