336 BARTRAM: TORTULA IN SOUTHERN ARIZONA 
ToRTULA RURALIS (L.) Ehrh. Widely distributed over the 
foothills and mesas, on the shaded banks of dry washes, on 
slightly shaded slopes or even on the open desert where it is 
usually sterile and depauperate. In the mountain canyons at 
altitudes above 4000 ft. it is usually replaced by the following. 
.  ToORTULA MONTANA (N. v. E.) Lindb. Readily distinguished 
from T. ruralis, as a rule, by the concave, hardly carinate leaves, 
erect spreading when moist, the less strongly recurved leaf 
margins and especially the smaller more obscure leaf cells in the 
upper part of the lamina which rarely measure over 10 y in 
diameter and often only 6 to 8u. Some forms show a slight 
tendency to intergrade with 7. ruralis in one or more characters 
but in this region, at least, the species surely represents a well 
defined segregate that replaces T. ruralis almost entirely in the 
mountain canyons. 
TORTULA ALPINA (Bry. eur.) Bruch. While this plant does 
not seem to have been credited to the North American flora 
heretofore, comparisons of various collections from Arizona 
with authentic European material of the species, generously 
supplied by Mr. Holzinger and Mr. Chamberlain, indicate that 
I’. alpina, in various forms, is widely scattered through the 
canyons and foothills of mountain ranges in the southern part 
of the state. In this arid country the collections from’ shaded 
ledges below 4000 ft., in the treeless foothills, are naturally 
xerophytic types, somewhat dwarfed and reduced in every way. 
As one works up the canyons into the oak belt above 4500 ft., 
the plants become more typical and at 6000 ft. or above, where 
moisture and shade are not lacking, the collections, in part at 
least, approach closely to the typical form of the species. The 
variations seem to be of degree rather than kind and present a 
close series of transitional forms ranging from the xerophytic 
types of low altitudes with reduced leaves, broadly obtuse or 
emarginate at the apex as in figures 12 and 13 of the accompany- 
ing plate to well developed plants of higher altitudes with larger 
leaves less broadly pointed, as in figure 14, which seem to closely 
approximate typical 7. alpina in every essential vegetative 
feature. Indeed these observations lead logically to the question 
of whether 7. alpina and T. laevipila might not better be treated 
as extreme forms of a single specific aggregate, modified by 
environment but connected by a series of transitional forms. 
