TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 



83 



The highest relative rates secured in the Jamaican plants were 0.758 

 for Dodonoea among sun readings, and 0.274 for Asplenium alatum 

 among shade readings. Among Mrs. Shreve's readings the highest 

 was a shade reading of 0.818 in a hot-house plant, the highest in an 

 outdoor plant being 0.353 for the branch of a tree in leaf. Livingston's 

 highest readings were 0.785 for AUionia and 0.371 for Boerhaavia. In 

 short, the highest of the sun readings in Jamaica, taken on one of the 

 most xerophilous shrubs, nearly equals the highest of the sun readings 

 taken by Livingston for AUionia, which is one of the many desert 

 ephemerals unable to withstand periods of rainless, sunny weather 

 for more than a fortnight. The maximum readings for Clethra and 

 Boerhaavia are similar, being 0.351 and 0.371 respectively, and those 

 for Alchornea and Tribulus happen to be identical: 0.263. A general 

 parallel is thus established between the relative rates in the summer 

 ephemerals of the desert and the most xerophilous of shrubs and trees 

 in the Blue Mountain region. The maximum rates of relative trans- 

 piration secured by Mrs. Shreve for Parkinsonia range, on the whole, 

 lower, for all of her experiments performed in the sun, than the maxi- 



Table 30. Relation of relative transpiration to increasing evaporation. 



Relative transpiration readings for three speeies grouped according to the evaporation rate 

 of the interval in which each transpiration reading was secured. The number of readings aver- 

 aged in each group is indicated. 



