970 The American Naturalist. [November, 
It is impossible to determine how long such subruderal 
formations have persisted. The size and thoroughness of 
establishment of Gutierrezia and Artemisia would indicate 
occupation for several decades. After a long period, however, 
it usually happens that Stipa comata, driving out the subruderal 
inhabitants, reconquers these trails. It is significant that the 
dark patches of Opuntia humifusa, or O. polyacantha so charac- 
teristic of this formation, never reappear with the Stipa. But 
even the speargrass is unable to resist the modifying influence 
of the trail, and its abnormally tall stems and compact growth 
find easy interpretation in connection with the ruts and ridges 
on which it grows. The old California trail is the most inter- 
esting example of this. Throughout the upper valley of the 
North Platte in Nebraska, this historic overland route is marked 
by such a zonal formation. From the base of Scott’s Bluff, the 
California trail, first travelled more than three-score years ago, 
and abandoned for over a score of years, “ angles ” southeast- 
ward in a broad band of innumerable ruts, painfully insistent 
in their matted cover of bleaching grass-stems. 
THE CRICKET AS A THERMOMETER. 
By A. E. DotBear. 
An individual cricket chirps with no great regularity when 
by himself and the chirping is intermittent, especially in the 
day time. At night when great numbers are chirping the reg- 
ularity is astonishing, for one may hear all the crickets in a 
field chirping synchronously, keeping time as if led by the 
wand of a conductor. When the numbers are so great, the 
resting spells of individuals are unnoticed but when the latter 
recommence they not only assume the same rate but the same 
beat as the rest in that field. The crickets in an adjoining 
field will have the same rate, that is, will make the same num- 
ber of chirps per minute, but with a different beat as one may 
easily perceive by listening. 
