216 The Botanical Gazette. [May, 
ness of climate??* Ifso, to means or extremes of dryness? It 
is to be noted that condensation can be more easily effected 
in the deserts than in cloudier climates, for the great cause in 
antagonism to condensation, 7. ¢., the need for a large spread 
of green surface, is here much less operative; for the slow 
growth of the plants requires less assimilation, and the intense 
and continuous light render possible a given annual amount of 
assimilation with a far smaller surface than is possible in 
cloudier climates. Hence condensation is absolutely easier 
to desert than other vegetation, and it may mean that the 
conditions are as not extreme as they appear judged by other 
standards. 
Passing now to internal anatomy, the first great problem 
is to study it in relation to external conditions. As one 
views Cactacez in collections, he is continually surprised at the 
apparent lack of relation between the development of the tis- 
sues and the supposed habits of the plants. Some forms,such as 
Rhipsalis, Phyllocactus and some Opuntias, though not very 
characters, how are the latter to be explained? Does tissue 
anatomy respond sensitively to changing conditions or does it 
not? Here, perhaps, better than anywhere else, is the op- 
portunity to delimit internal growth conditions from those of 
‘tadaptation.” A comparative anatomy of the family, stud- 
ied in relation to life-conditions, and introducing compatl- 
sons with the characteristics of other desert families, would be 
of great value. 
The very common collenchymatous hypoderma is proba- 
- upright; Cereus testudo. 
6 pled weneee cprreie vi ta flexed: some Rhipsalis species. _ i 
d. Piyllocladia, two-ribbed flat shoots: Phyllocactus, Rhipsalis, Epiphyllum. 
e. Flattened ribless shoot $ ae BRA yowhee Ba puntia Brasiliensis- 
; : f ri : Echinopsis. upright Echinocereus, Echino- 
£. Sphere form (including! cactus, Astrophytum, Melocactus, etc. é 
short columns) tubercled: Mamillaria, Leuchtenbergia, Pelecy 
phora, Anhalonium. Z to 
Noll has given (Flora 77: 353-356. 1893) exact data on relation of form 
transpiration. 
