Deserts 
strange modification of the protoplasm which enables 
them to resist heat, and also to breathe internally without 
opening their pores, which might allow the dangerously 
dry air to enter their bodies. 
In the American desert a thermometer placed in the 
body of a cactus (Cereus sp.) showed a temperature of 
45° to 46° C. Indeed their -body temperature is often 
above that of the earth near them. Askenasy found 
that when the sand showed only 43° to 44° C., the leaf 
of a Sempervivum had a temperature of over 51° C. 
In one day they are subject to extraordinary fluctua- 
tions. At7 to 8 A.M. the leaf of Sempervivum tectorum 
showed 13° C., and at 2 to 3 P.M. it was at 49.6°C., 
which means a difference of over 33° in a single day. 
Their exact system of keeping alive in deserts is not 
understood. In dry weather Cereus and some other 
cacti seem to shrink together so as to show deep longi- 
tudinal grooves. This shrinking will close up their 
stomata or breathing spores.® 
In wet or misty weather they expand so that the 
grooves become shallower, like those of a camera-case 
when drawn out. Then the moist air penetrates into 
a curious system of air channels, which branch in and 
- -out amongst the green assimilating cells. At such 
times they are actively growing and even forming 
(Echinocactus sp.) green leaves, which drop off as soon 
as the drought begins.‘ 
They have the curious property of being able to give 
out carbonic acid without taking in oxygen. One does 
not like to charge them with alcoholism, but it seems 
that they must somehow produce oxygen for respira- 
tion without allowing the dry outside air to enter the 
body. So it is quite possible that some kind of alcoholic 
fermentation is really going on within these innocent- 
looking fleshy stems. 
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