DEPARTMENT OF BOTANICAL RESEARCH. 71 



Gasteria, and Massonia have a notable water-balance. The water-storage 

 capacity of Aloe, Cotyledon coruscans, and Gasteria is in the leaves, while that 

 of Cotyledon paniculata is in the very much enlarged and stout stem, and 

 that of Massonia in the underground enlarged portions. Gasteria and 

 Massonia are perennial herbaceous forms. Although all of these forms have 

 relatively low transpiring indices, as indicated by the table, the indices prob- 

 ably vary with the seasons, as well as with a variation of different environ- 

 mental physical factors, and with the physiological condition of the individual. 

 Thus, the relatively high transpiring index of Aloe schlechteri was obtained 

 at the time of flowering, in late winter, and when evaporation rates, as told 

 by readings of the atmometer, were relatively low. That of A. striata, on 

 the other hand, was in midspring, when the species was past flowering and 

 when the high evaporation rate of spring and summer was already close at 

 hand, as foreshadowed also by the atmometer. Studies on Cotyledon, on the 

 other hand, were conducted in midspring, and both species were growing 

 under parallel environmental conditions. In both species it appears possible 

 that the maximal indices given may indeed represent the highest for the 

 entire year. The slight difference in the magnitude of the index as between 

 the species with succulent perennial leaves, C. coruscans, and the species 

 with deciduous leaves and succulent stem, is probably significant. In the 

 latter, C. paniculata, leaf fall was proceeding four weeks after the tests on it 

 were made. This species is confined to regions where the water-relations 

 are relatively good. But a similar result as between species with water- 

 balance in the leaves and in the stem was obtained in Gasteria and Massonia, 

 and it may be characteristic of such morphological differences. 



The sclerophyllous species have all a fairly high index of transpiring power, 

 although they vary considerably among themselves in this regard. Thus, 

 Protea neriifolia, which occurs where the rainfall is relatively high, was 

 observed to have, in late October, a relatively high index. Other species 

 which were studied during the same time, such as Euclea, Euyrops, and Rhus, 

 were found to have much lower indices than that of Protea, but at the same 

 time much higher than that of the species with water-balance. Rhus lancea 

 occurs along streamways at Matjesfontein, rainfall 6.96 inches, and Euyrops 

 laterifolius under relatively favorable moisture conditions in the same vicinity. 

 It is to be noted that the minima indices of these species approximate the 

 maxima of those previously referred to. Shrubs with perennial leaves may 

 show equal or very unequal transpiring power of the two leaf-surfaces. In 

 Gymnosporia the former condition appears to obtain, and in others, notably 

 in Euyrops, Rhus, and Protea, the latter. In the case of Euyrops and Rhus, 

 the ventral surface has the larger index, but in Protea the maximum index 

 was obtained on the dorsal surface. In Protea, as the leaf matures it assumes 

 a permanent erect position with the ventral surface facing outward and 

 hence especially exposed to the wind, to light, etc. The difference in index 

 of transpiration between the dorsal and ventral leaf-surfaces in Protea is 

 less marked in young leaves. The transpiring power also increases toward 

 the leaf-tips. The greatest difference between the two leaf-surfaces in trans- 

 piring power was found in Gymnosporia, in which the ratio was about 20 to 1 ? 

 denoting little water-loss from the dorsal surface. The differences in trans- 

 piring power of leaves on one and the same specimen, as well as differences 



