434 



NA TURE 



{_March ii, 1886 



having also been recently worked out, the three floras 

 together enable a fairly accurate estimate to be formed of 

 the nature and extent of the vegetation of the middle 

 regions of temperate North America from ocean to 

 ocean. Thus Gray's manual takes in the States between 

 the Atlantic and Mississippi, which lie north of Tennessee 

 and North Carolina ; that is, approximately between 

 lats. 36i^ and 46' N., and is essentially the vegetation of 

 a wooded region with high-lands towards the coast. The 

 Rocky Mountain manual occupies a rather smaller area, 

 comprising the States of Colorado, Wyoming, Montana, 

 Western Dakota, Western Nebraska, and Western 

 Kansas. Its southern and northern limits are on the 

 same parallel as those of Gray's " Flora," and its eastern 

 limits (the looth meridian) is nearly parallel to and as 

 long as Gray's western, and distant from it about 400 

 miles. Its western frontier is a very irregular one, follow- 

 ing the north-western and south-eastern direction of the 

 great mountain plateau ; and borders the Pacific States 

 of Washington and Oregon, and the interior ones of 

 Nevada and Utah. It is essentially an Alpine and prairie 

 vegetation ; probably most or all of it is above 4000 feet of 

 elevation, with mountains attaining a maximum of over 

 14,000 feet (Mount Gray). The Californian flora, again, 

 does not occupy half the area of either of the others. It 

 extends rather further south, to lat. 35°, and only to 45° N. 

 Though only 200 miles in average breadth, it is infinitely 

 richer than both the others combined, having a mountain 

 flora — the Sierra Nevada— throughout the length of its 

 eastern boundary, a coast flora along the Pacific, a liill 

 flora along a coast range, and a valley flora between the 

 latter and the Sierra Nevada. 



Comparing the areas thus limited with that of the 

 whole breadth of what may be regarded as temperate 

 North America (in contradistinction to the cold British 

 possessions to the north of 48^ and the hot ones to the 

 south of 35°), it will be seen that they together cover 

 nearly four-fifths of the breadth of the continent, of 

 which 1200" miles are in the limits of Gray's "Flora," 

 700 in Coulter's, and (though not in the same parallel) 

 200 in the Californian. The strips of country not included 

 are, the wooded region west of the Mississippi, and the 

 prairies between the latter and the lOOth meridian, and the 

 region of the Great Basin, between the Rocky Mountains 

 and the Sierra Nevada. Neither ot them can, however, 

 be expected to add much to the sum of the three floras 

 now under consideration, for on the one hand the 

 western wooded region of the Mississippi cannot add 

 much to Gray's flora or the eastern prairies to Coulter's ; 

 and on the other hand, as the Rocky Mountain flora 

 takes in the plants of the western fringe of the Great 

 Basin, and the Californian its eastern fringe, the inter- 

 mediate region cannot add very much to what these two 

 floras contain. 



Dr. Gray 1 has in various essays admirably discussed 

 the characteristics of the three longitudinal zones of 

 North American vegetation, and clearly indicated their 

 composition and relations. In no region of the northern 



• "Statistics of the Flora of the Northern United States" {Ameruatt 

 "Journat of Science ami Arts, vol. xxiii.) ; " Remarks concerning the Flora 

 of North America " (American yoiirnal of Scieiue and Arts, vol. xxiv.); 

 "Vegetation of the Rocky Mjuntain Region " (Bulletin of the United 

 States Geological and Geographical Survey, val. vi. No. i, i88r); " Charac- 

 ■ ,^^ Flora" (British Association Reports, 

 Journal 0/ Science, va\. xxviii. 1884). 



hemisphere, nor perhaps anywhere on the globe, can 

 three parallel meridional floras so different in their aspect 

 and elements be found within such narrow limits, as the 

 middle unforested zone of North America separating two 

 heavily forested ones, the latter differing from one another 

 by hundreds of genera and thousands of species. 



The richness of the three floras as expressed by 

 genera and species is, in round numbers — 





Rocky Mountain Flora 

 Eastern United .States 

 Californian 



Species (European) 



500 1750 (300) 



660 2150 (370) 



764 3786 (225) 



A striking difference between the Pacific and Atlantic 

 floras is in the relative numbers of the two primary groups 

 of Dicotyledons : the Polypetalae and Monopetalae, 

 which in California are as 'eighteen to ten, but in the 

 Eastern States nearly equal. In both the Incompletae 

 amount to about one-third of the Monopetala;, in which 

 respect the Rocky Mountain flora assimilates to the 

 Eastern one. But the most remarkable difference 

 between the three floras is in the relative proportion of 

 Monocotyledons and Dicotyledons, which is about I : 2'i8 

 in the Eastern United States ; i : 3 in the Rocky Moun- 

 tains ; and I : 4"9 in California. This is mainly due to the 

 greater number of Junces, Cyperaceas, and Gramineae in 

 the Rocky Mountains and Eastern States, and the abnormal 

 excess of various Dicotyledonous families in California. 

 So too with the proportion of genera to species : it is 

 nearly the same in the Rocky Mountains and Eastern 

 States (i : 3^5 and l : 3'3), but in California, owing very 

 much to the number of monotypic genera, it is nearly as 

 1 : 5. 



Regarding the composition of the Rocky Mountain 

 flora, the most remarkable facts are the number of Com- 

 positae, amounting to one-fifth of the Phanerogains, thus 

 far exceeding the proportions in the Eastern United 

 States (about one-seventh), and in California (about one- 

 eighth). Of this order nearly forty genera do not occur 

 in the Eastern States. Leguminosa; come next in order 

 of number of species, as they do in California, where, 

 however, they are fewer in proportion to the whole 

 flora. These, with Graminese, Cyperacese, .Scrophu- 

 larineas, and Rosaceas, which follow next in order ot 

 numbers (six families in all), embrace half the Rocky 

 Mountain Phanerogamic flora. In the Eastern United 

 States half of the flora consists of seven families, of 

 which the five first are the same as in the Rocky Moun- 

 tain flora ; but Scrophularineae are replaced by Ericeoe, 

 and Ranunculaceaj are to be added. In California, oia 

 the other hand, species of no fewer than thirteen families 

 must be added together to embrace half the flora. 



But the most conspicuous difference to the eye between 

 the vegetation of the Rocky Mountains and the Eastern 

 .States consists in the absence in the former of almost 

 all the Conifers and Cupulifers of the latter, together 

 with the whole Orders of Magnoliacea;, Tiliaceas, Juglan- 

 de.i;, Platanaceas, and Droseraceas, and the rarity of 

 Hypericineaj, Rubiaceaa, Lobeliacese, Ericese, Labiatae, 

 and Orchidea:, and of water-plants generally. On the 

 other hand, there is in the Rocky Mountains a much 

 greater abundance of Cruciferas, Portulaceae, Loasacere, 

 Cactaceae, Polemoniacese, Borragineae, Solanaceas, Che- 

 nopodiaceae, Polygoneae, and Nyctagineas, — all show- 



