208 



SCIENCE 



[N. S. Vol. XXVII. No. 684 



8. One with center of head gi-een instead 

 of purple. 



Plant Zones of the Mountain Lakes in 

 Northern Colorado: Francis Ramalet 

 and W. W. Robbins. 

 In the Rocky Mountain region of north- 

 ern Colorado, the lakes of the subalpine 

 and alpine districts are of the morainal 

 type, while those of the montane zone are 

 chiefly meander lakes. Around these lakes 

 zonation is well developed in cases where 

 there is an accumulation of silt. 



In a typical morainal lake studied by the 

 writers, there is a Carex zone surrounded 

 hy a Salix-Betula zone. Among the more 

 prominent plants in the former zone are 

 Dodecatheon and Clementsia besides vari- 

 ous grasses and sedges. Mosses occur here 

 also, chiefly Polytrichum, Milium and 

 Sphagnum. In the Salix-Betxda zone there 

 are such plants as Elephantella, Pedicidaris 

 and a few orchids. This zone is sur- 

 rounded by a coniferous forest. 



A meander lake at about 9,000 feet alti- 

 tude, showed four zones: (1) Carex; (2) 

 Salix-Betula; (3) Dasiphora; (4) Campa- 

 nida. Still another meander lake (alti- 

 tude 8,000 feet) had three zones: (1) 

 Carex; (2) Thermopsis; (3) Campamda. 

 Back of these zones in this particular case 

 there is a belt of grassland before the conif- 

 erous forest is reached. 



Lakes above timber line show no zona- 

 tion. In all lakes of the montane and sub- 

 alpine districts, pond weeds occur and yel- 

 low pond lilies in many. There is an 

 entire absence of cattail and bulrush vege- 

 tation. 



It is worthy of note that in general the 

 pondside plants have come down from 

 higher altitudes and the plants of dry 

 situations have come up from lower alti- 

 tudes. In other words, the mountain 

 mesophytes are largely boreal forms while 

 the xerophytes show austral affinities. 



Bock-ridge Vegetation of Northern Colo- 

 rado: Francis Ramalet and W. W. 

 Robbins. 



The sedimentary rock ridges in northern 

 Colorado have a striking appearance due to 

 the considerable dip of the strata and the 

 numerous faults and folds. Sharp escarp- 

 ments, deep gulches and irregular erosion 

 lines make the country rough and rugged. 

 A remarkable scrub formation of moun- 

 tain mahogany (Cercocarpus parvif alius) 

 occurs on these ridges, being generally 

 quite dense where there is little soil and 

 frequently stopping as an abrupt line near 

 the foot of a hill or ridge. 



At the line of contact between the gran- 

 ites and the conglomerates there is usually 

 a broad lateral valley with rather fine- 

 grained compact soil. This supports a 

 grassland formation with no trees or 

 shrubs. The granite hills to the west have 

 a scattered covering of pines, various 

 shrubs, grasses and perennial herbs. East 

 of the lateral valley are the sedimentary 

 rock ridges with their dense scrub of moun- 

 tain mahogany and a few scattered pines. 

 In the deep gulches, Douglas spruces and 

 deciduous mesophji;ic shrubs occur just as 

 in the canyons of the granite foothills. 



The rock ridges with much lime in their 

 composition show a very open formation of 

 Cercocarpus, the shrubs being often eight 

 or ten feet apart, but on the sandstone the 

 plants make a close stand very diifieult to 

 climb through. Cercocarpus grows only 

 on a dry, rocky substratum and is replaced 

 by grassland where there is more soil and 

 moisture, while its place is taken by meso- 

 phytic shrubs, trees and grasses in moist 

 shaded situations where there is an ac- 

 cumulation of humus. 



A careful study was made of one square 

 mile of territory at the contact of the 

 granites and sedimentaries. This territory 

 was mapped and the vegetation charted 



