LAKE TITICACA. 265 



supplied by other species, which have in like manner 

 their equatorial and polar limits. These are not, how- 

 ever, so numerous as those which die out, there being 

 no rule more general than the decrease of generic and spe- 

 cific forms in passing from temperate zones to arctic or polar 

 ones. 



There is a similarity in many respects between the vege- 

 tation of alpine tracts and that of high latitudes, but not 

 an identity, the condition of the two regions differing in 

 some essential particulars. No more apt illustration of 

 this fact is needed than that adduced by Meyen, of 

 Titicaca. This alpine lake, situated on the plateau of 

 Chuquito in southern Peru, at the elevation of 12,700 feet, 

 is surrounded by a rich and beautiful vegetation, which 

 flourishes under a perpetual spring. On its banks a popu- 

 lous community, inhabiting magnificent cities, is supported 

 by a fertile soil, yet trees are wanting in the country ; 

 whereas we have seen that the pine forest extends in North 

 America to the 69th parallel beyond the limits of the 

 cerealia. On the shores of Lake Titicaca barley and oats 

 grow, but wheat does not succeed, and maize is raised only 

 by artificial heat. In respect of these products, therefore, 

 its climate agrees with that of Fort Simpson on the 62nd 

 parallel. Its summer heat, which, according to Meyen, 

 ranges between 52° and 66° Fah., is more equable than 

 that of Fort Simpson which has a mean daily summer 

 temperature of about 59° Fah., with a mean at noon of 

 70° Fah.; and a range of from 90° Fah. down to below the 

 freezing point. 



It is necessary to remark, however, that the decrease of 

 vegetable forms with an increase of latitude has more 

 analogy to that which is observed on a lofty isolated moun- 

 tain than on an elevated plateau ; and plants actually grow 

 on the summits of the White Mountains of New Hamp- 



