AN INVESTIGATION OF THE CAUSES OF 



AUTONOMIC MOVEMENTS IN 



SUCCULENT PLANTS 



EDITH BELLAMY SHREVE 



Tucson, Arizona 



(Concluded) 

 II. 



Livingston and Brown 4 found that in the climate of southern 

 Arizona (the habitat of the plants used in this research) "green 

 plants when subjected to relatively great diurnal evaporation 

 intensity, at least frequently, exhibit a marked fall in foliar mois- 

 ture content by day and a corresponding rise by night." They 

 found this true for several species of thin-leaved plants and for 

 one succulent, Trianthema portulacastrum., but failed to find it 

 in two species of thick leaved xerophytes (Covillea glutinosa 

 and Prosopis velutina). However, the present author 5 found 

 it for Parkinsonia microphylla, which is a very thick leaved 

 perennial. Lloyd 6 found the same result with leaves of Fou- 

 quieria splendens and working with cut shoots of the same 

 species on burettes, he obtained a difference between water in- 

 take, as measured by the burette, and transpiration loss, as meas- 

 ured by loss of weight, which was negative for the day and posi- 

 tive for the night. In order to test the matter for this cactus 

 experiments 9 and 10 were carried out. 



4 Livingston, B. E. and Brown, W. H., Relation of the daily march of trans- 

 piration to variations in the water content of foliage leaves. Bot. Gaz. 53: 

 309-330, 1912. 



6 Shreve, E. B., The daily march of transpiration in a desert perennial. Car- 

 negie Inst. Wash. Pub. No. 194, 1914. 



6 Lloyd, F. E., The relation of transpiration and stomatal movements to 

 the water content of leaves of Fouquieria splendens. The Plant World 15: 1-14, 

 1912. 



331 



