Periodical Literature. 75 



Pseitdotsuga mucronata-Picea engelmanni formation were due 

 to the projection of its higher and more characteristic habitat into 

 the area characteristic of Pseitdotsuga and that, therefore, the 

 author gives more prominence to altitude than to habitat in dis- 

 tinguishing the formations. 



The measurements of temperature, relative humidity, and soil 

 water content within these various formations are interesting, 

 but they are not conclusive because of their short duration. For 

 example, the most extensive records are those of air and soil 

 temperatures. None of these records in any one formation ex- 

 tends through more than five days and yet the author concludes 

 that mountain zonation is due entirely to temperature. 



C. D. H. 



The Forest Formations of Boulder County, Colorado. Botanical Ga- 

 zette, 1907, 44, pp. 321-352. 



A posthumous article by Hofrat Friedrich 

 Growth brings a series of measurements with one of 



Energy his auxanometers (see description in F. Q., 



of vol. IV, p. 52) on a number of species. 



Trees. The first and apparently hitherto only in- 



vestigator of the growth energy of trees 

 was Krabbe who came to the following results: 1. The force 

 with which diameter growth takes place amounts in conifers to 

 at least 10, in broadleaf trees 15 atmospheres. 2. At the time of 

 summerwood formation this force is still 8 to 10 in conifers and 

 12 to 15 in broadleaf trees. 3. A limit of growth energy could 

 not be determined. 



A description of the apparatus is given: A spiral spring of 

 tested capacity in a suitable framework and provided with a cen- 

 timeter scale is attached tightly to the tree, and the pressure read 

 off. The adjustment, it was found, was not quite simple, if the 

 experiment was to be precise, but eventually all difficulties were 

 overcome. As long as the elasticity of the spring is not ap- 

 proached by the growth energy the spring is compressed, and 

 automatically a constantly increasing pressure exercised upon 

 the wood. With increasing pressure the increment must become 

 slower, and when equality of forces is reached, it ceases, the 

 nonius, which is read off twice daily, does not move any more, 

 the limit of pressure against which the cambial activity is able 



