754 BIOGRAPHICAL MEMOIRS. 



table Physiology," also, was published first iu 1868, as an accompani- 

 ment to the Manual, and has had its five editions at nearly the same 

 dates. The first volume of another companion work to the Manual was 

 issued in 1848, — his " Genera Illustrata," containing descriptions of the 

 genera of the United States Flora, wilh illustrations of great beauty 

 by I. Sprague; and in 1849 a second volume was published, carrying 

 the works nearly to the Leguminosfe; and here it stopped, on account 

 mainly of the expense. His " Field, Forest, and Garden Botany," a 

 useful flora for schools, came out in 1868; and the charming smaller 

 volumes, " How Plants Grow " and " How Plants Behave," respectively 

 in 1858 and 1875. The latter was prompted by Darwin's works on 

 Insectivorous Plants, the Orchids, and Dimorphism, and both are well 

 adapted to the young student and all uninitiated readers. 



Besides the subjects of Gray's investigations already mentioned, two 

 others of a wider philosophical character interested him deeply : one, 

 in which he was pioneer, the other, the Origin of Species, after Darwin. 



The first of these subjects was the Geographical Distribution of 

 Plants, and particularly the species of the northern United States 

 both within and beyond the bounds of the continent, and the bearings 

 of the facts on variation and origin. 



His first paper on the subject is contained in volumes xxii and xxiii 

 of the American Journal of Science, the numbers for September, 1856, 

 and January and May, 1857. It was written partly in compliance with 

 the request of "an esteemed correspondent" for a list of American 

 alpine plants, who, as now appears, was Darwin. Darwin's Life con- 

 tains, on page 420, the letter, and shows that its date was April 25, 

 1855; and, also, a second letter of June 8, 1855, which opens thus: "I 

 thank you cordially for your remarkably kind letter of the 22d ult., and 

 for the extremely pleasant and obliging manner in which you have taken 

 my rather troublesome questions. I can hardly tell you how much your 

 list of alpine plants has interested me." And then Darwin puts more 

 questions to his genial correspondent. 



The long paper, modestly entitled " Statistics of the Flora of the 

 United States," contains numerous tables, comparing as regards plants 

 the northern United States with Europe on one side, and Asia and 

 Japan on the other; the eastern part of the country with the western, 

 and with the adjoining continents in the north temperate zone; the 

 plants of alpine and subalpine regions in the northern United States, 

 and their distribution southward and eastward and westward over the 

 other continents; the distribution of species common to this country 

 and Enrope, as to size of orders and genera ; also, as regards related 

 and representative species, and the same for eastern and western 

 America; lists of species of widely sundered habitation; with numer- 

 ous other points, and abundant explanatory remarks; making thus a 

 thorough philosophical digest of the subject of geographical distribu- 

 tion, having all the completeness as respects the northern United 



