i PHYSIOLOGY OF THE COCO-NUT 9 



thin-walled. When the leaflet is well stored with water, 

 the cells of the hinge are turgid, swollen up as large as 

 possible ; each hinge then raises its half of the pinna, 

 making the whole leaflet as wide as it can be. When 

 the amount of water in the leaf is decreased, the cells of 

 the hinge are quick to feel the loss, and with any loss 

 of water their size decreases. This results in a lowering 

 of each side of the pinna, making the whole pinna 

 narrower, and so lessening the exposure to the sun. 

 The transpiration will be greatest if the tree is at all 

 times so well supplied with water that the hinges do 

 not let the sides of the pinna lower. 



The transpiration is made active by light, warmth, 

 dryness of the air, and wind. It is hindered by dark- 

 ness, cold, and moistness and stillness of the air. The 

 most important of the factors influencing the transpira- 

 tion is light. A light haze across the sun — too light 

 to be called a cloud — will immediately reduce the trans- 

 piration by one-third or one-half. A cloud heavy enough 

 to conceal the sun will promptly cut it down to about 

 one-quarter of what it is in direct sunshine. All shade 

 has, of course, the same effect, and it makes no difference 

 whether it comes from a cloud, or a mountain, or some 

 shade tree, or another coco-nut planted too near. Every 

 leaf or part of a leaf which is in the shade has its 

 transpiration cut down to a quarter of what it might 

 be, and therefore gets only a quarter of the food it 

 might get dissolved in the water. 



During the whole night the whole transpiration is 

 not one-tenth as much as during one hour of full sun- 

 shine. Diffuse light increases the transpiration chiefly 

 by causing the stomata to open. The great added action 

 of direct light is chiefly due to the heating of the leaf. 

 The following table gives the temperatures observed 

 during one day, the first column giving the temperature 

 in the shade ; the second, the temperature in direct sun- 

 shine ; and the third, the temperature shown by a 

 thermometer placed near the second, but with a coco- 

 nut leaflet tied around its bulb. 



