258 BOOKS AND CURRENT LITERATURE 



works on forage grasses and grazing ranges have appeared from Experi- 

 ment Stations in the west. With these faults the book is nevertheless 

 valuable and should be in every general library, and in the libraries 

 of botanists, agrostologists and progressive agriculturists. It can 

 hardly find a place in our schools, however, as a text-book. — J. J. 

 Thornber. 



Internal Temperatures of Desert Plants. — Pearson has in- 

 vestigated 1 the internal temperatures of Euphorbia virosa and Aloe 

 dichotoma, two of the commonest succulents of Great Namaqualand, 

 carrying on his work in their natural habitat at 4200 ft. elevation. 

 Aloe possesses a soft woody stem rich in water. The daily range of 

 temperature at the center of the stem is as much as 24° or even 30° F., 

 the minimum being approximately that of the air, and the maximum only 

 3° to 7° above atmospheric shade temperature — or up to 101°. Euphor- 

 bia virosa has a large central air cavity crossed by numerous partitions 

 containing lactiferous vessels. The temperatures of the gas-filled cavi- 

 ties have a daiby range of as much as 24° and even 49° F., extending 

 from minima which are practically those of the atmosphere to maxima 

 which are from 19° to 25° higher than those of the air, carrying the in- 

 ternal maximum as high as 125° F. The wounding of Aloe causes a 

 tardy fall of temperature, which appears to be due to evaporation from 

 the cut surfaces. The wounding of Euphorbia causes an immediate fall 

 of the internal gas temperature, together with a more prolonged local 

 lowering of temperature. The wounding of Euphorbia is accompanied 

 by a copious exudation of latex and by a partial release of the internal 

 gas pressure, which is normally somewhat higher than atmospheric 

 pressure. Pearson attributes the sudden fall of temperature to the 

 expansion of the internal gases when released by the wound, and re- 

 gards the outflow of latex as accelerated by the influence of the pressure 

 disturbances on the lactiferous partitions. Evaporation from the 

 exuded milk causes a local lowering of temperature until the hardening 

 of the surface takes place through formation of caoutchouc. The pres- 

 sure of the internal gases is suggested as having a function in assisting 

 mechanical ridigity and in increasing the flow of latex. The sealing 

 of wounds by latex in Euphorbia is shown to lessen its liability to inju- 

 rious after-effects, as compared with the non-lactiferous Aloe. — Forrest 

 Shreve. 



Pearson, H. H. W., Observations on the Internal Temperatures of Euphor- 

 bia virosa and Aloe dichotoma. Ann. Bolus Herb. 1: 41-66, Nov. 1914. 



