114 BOTANICAL GAZETTE. 



largest orders being Composites (143 species), Cyperacece (105), 

 Graminece (88), Ro&icece (52), Legumlnosce (45), Menthacece (which 

 name looks unnatural -39), Riinancidaceai (36), Oruciferce (36), 

 Orchidacece (34), and Liliacece (31). The largest genera are Carex 

 (72 species), Solidago (20), 4sfcr (19), Polygonum (16), SWmc (14), 

 Potamogeton (12), KMa (11), Habenaria (10). 



The Timber Line.— In Dr. Rothroek's valuable report on 

 botany, recently published by the '"Surveys West of the 100th 

 Meridian, 1 ' the anchor quotes Dr. Englemann's statement that 

 "there is little or no increase in altitude in the timber line toward 

 the equator, in our western hemisphere, south oi the 41st parallel 

 of north latitude. 11 



This statement is approximately true regarding the Rocky 

 Mountains, owing, however, not to any general principle, but to 

 what may be termed an accident of topography. Even here a 

 decided rise is observable from 41° to 39° of latitude. In the Sierra 

 Nevada, the Basin and Wahsatch Ranges, the statement does not 

 hold good, the timber line rising rapidly as the latitude decreases. 

 Again, on the volcanic peaks of the Mexican plateau, the timber 

 line is higher by several thousands of feet than it is anywhere in 

 the United States. 



Barring the prohibitive circumstances of absence of soil and 

 moisture, the height of the timber line is purely a question of 

 temperature. The latter is a function of the latitude, the eleva- 

 tion, and the mass, of the country in the neighborhood. A great 

 mass of country, if raised to a considerable height above the sea, 

 as in the case of the great Cordilleran plateau of the West, carries 

 up with it, to a certain extent, the isothermal* A glance at Mr, 

 Schott's admirable isothermal charts amply illustrates the general 

 fact. Washington, D. C, has a mean annual temperature of 55° 

 Fah., while Denver, Col., a fraction of a degree farther north, and 

 at an elevation of 5,300 feet, has a mean temperature, not of 37°, 

 as the height might indicate, but of 49°. 



Therefore, in considering the height of the timber line, we 

 must regard the mountain ranges in connection with the plateau 

 upon which they stand, their latitudes, heights, and masses, or 

 what, in a measure, sums up thase three, their temperatures, 

 as it is by these that its height is determiued. 



Looking at the subject from this point of view, a fair compari- 

 son may be instituted between the timber line in different latitudes 

 and on different ranges in the same latitude. 



The actual elevation above the sea level of the timber line in 

 the Cordilleras of North America ranges from 6 or 7,000 to 12,000 

 feet. It is lower in the Coast and Cascade Ranges of Washington 

 Territory, where it is at about the former figures. Following the 

 Cascade Range southward into Oregon, the timber line rises to a 



