tJie Yellowstone National Park. 55 



The excellent Flora of the Yellowstone National Parh^ by 

 Mr. Frank Tweedy has been made the basis of all comparisons 

 between the fossil and living floras. According to Tweedy 

 the present flora embraces 69 natural orders, 273 genera and 

 657 species. The fossil flora embraces 33 orders, 63 genera, 

 and 147 species. The living flora has therefore 4 genera to each 

 order and 2*4 species to each genus, while the fossil flora has 

 not quite 2 genera to each order and 2*3 species to each genus. 

 The relative proportion between the orders, genera and species 

 is shown to be approximately the same in the living and Terti- 

 ary floras. A still further comparison shows that there are a 

 fraction more than twice as many living as fossil orders, 4*3 

 times as many living genera and 4*6 times as many species. 



On comparing the orders in the two floras it is found that 19 

 of the 33 fossil orders are not represented in the living flora.f 

 It is found that such important orders as the Juglandaceee, 

 Fagacese, Ulmacese, Magnoliaceee, Lauracese, Platanacese, 

 Anacardiacese, Celastracese. Yitacese, Sterculiacese, Tiliacese, 

 Araliacese, Ebenacese, and Oleacese, are not represented 

 in the present flora. In other words there are no wal- 

 nuts, hickories, oaks, beeches, chestnuts, elms, magnolias, syca- 

 mores, sumacs, grapes, lindens, azalias, persimmons, or ashes at 

 the present day. 



The dominant elements in the living flora are the abundant 

 coniferous forests, yet only eight species are present and of these 

 only five are at all common, and 65 per cent, of the whole con- 

 iferous growth is made up of one species {Pinics Murrayana). 

 The fossil flora is represented by thirteen species, or nearly 

 twice as many as the living. Among them was a magnificent 

 Sequoia that was closely allied to the living Sequoia semper- 

 virens of the Pacific coast. It had trunks ten feet in diameter, 

 and there are indications that they were of great height. 

 There were also two well-marked species of Sequoia known 

 from the leaves and a number of supposed Sequoia cones. 

 The pines were in abundance, no less than seven species having 

 been detected. Of these two are known from the leaves, three 

 from beautifully preserved cones and two from the internal 

 structure of the trunks. 



The living deciduous-leaved trees and shrubs of the Yellow- 

 stone Park are conspicuously few in number. There are two 

 species of Betula, two of Alnus, seven of Salix, two of Popu- 

 les, one of Acer, four of Yaccinium, five of the order Capri- 

 foliacese, two of Cornacege, two of Kosacese, etc. Perhaps the 

 most conspicuous tree is the quaking aspen {Pojpulus tremu- 



*Was"h., 18^6, pp. 1-78. 



f In the list of orders given above those not represented at the present day are 

 marked with an asterisk. 



