234 DAVENPORT ACADEMY OF NATURAL SCIENCES. 



finds its way to the West Branch. The moraines often have their 

 peculiar plants. The soil is extremely dry on the surface and we find 

 here such grasses as Poa nemoralis , P. Bucklcyana, Festuca ovina, 

 Sedum sienopetalum, Antennaria dioica and Draba streptocarpa. Close 

 to the moraine are large flats where there is considerable moisture. 

 Here Savastana odorata, Viola palustris, Mertcnsia sibirica, Phleiim 

 alpitmm, Deschampsia caespifosa, and Potentillafruticosa, Kalinia glauca 

 var. microphylla grow in great quantities. On the shaded side of these 

 moraines considerable snow still remained on the first of July; here 

 we found Kalinia glauca var. microphylla, and Viola palustris. 



The predominating tree at this elevatian is Pinus Murray ana. The 

 Engelmann Spruce occurs only in the canons, and here too we again find 

 Poa Wheeleri, and Phlcuni alpiuum is one of the most cf)mmon grasses in 

 such places. Elk Mountain, with an approximate elevation of ii,ooo 

 feet, contains the usual alpine plants. The timber line begins at about 

 10,500 feet. Just below it the Engelmann Spruce forms a belt of tim- 

 ber. Of the grasses we may enumerate: Poa Suksdorjii, P. Fendleriana 

 in dry open woods, elevation 10,000 feet, P. rupeslris, P. Wheeleri. 

 Associated with these plants we note Donglasia niontana, Silene acaulis, 

 Primula Parrvi, Dryas ociopelala, Trollius laxus, and Merlensia alpina. 

 It is interesting to observe that some western representatives reach 

 the eastern borders of the Rocky Mountains. 



VARIATION AS TO ALTITUDINAL DISTRIBUTION. 



Altitude is an important factor in the distribution of plants. It has 

 long been recognized that animals and plants are not universally dis- 

 tributed over the earth's surface but follow certain lines, as C. Hart 

 Merriam^i' says: " Which lines indicate a change in temperature 

 uncongenial to the species. * * * The temperature selected as 

 probably fixing the limit of northward distribution is the sum of effec- 

 tive heat for the entire season of growth and re|jroduction, for it has 

 been proved experimentally and long recognized by phenologists that 

 many species of plants require a definite sum total of heat in order to 

 successfully perform the several vital functions of leafing, blossoming 

 and fruiting, and that such plants cannot mature their seed until a 

 particular sum of heat is attained." Merriam holds that the geo- 

 graphic distribution of animals and plants may be expressed as follows: 



* The Geological Distribution of Animals and Plants in North America. Year Book, U. 

 S. Dept. of Agriculture, 1894:211. 



