1867-1882] ISLAND LIFE 25 



history in petto ; but I can see one very great difficulty that Letter 397 



you yourself ought to figure most prominently in it ; and this 



you would not do, for you are just the man to treat yourself 



in a dishonourable manner. I should very much like to see 



you discuss some of Wallace's views, especially his ignoring 



the all-powerful effects of the Glacial period l with respect to 



alpine plants. I do not know what you think, but it appears 



to me that he exaggerates enormously the influence of debacles 



or slips and new surface of soil being exposed for the reception 



of wind-blown seeds. What kinds of seeds have the plants 



which are common to the distant mountain-summits in 



Africa ? Wallace lately wrote to me about the mountain 



plants of Madagascar 2 being the same with those on mountains 



in Africa, and seemed to think it proved dispersal by the wind, 



1 " Having been kindly permitted by Mr. Francis Darwin to read this 

 letter, I wish to explain that the above statement applies only to my 

 rejection of Darwin's view that the presence of arctic and north temperate 

 plants in the southern hemisphere was brought about by the lowering of 

 the temperature of the tropical regions during the Glacial period, so that 

 even ' the lowlands of these great continents were everywhere tenanted 

 under the equator by a considerable number of temperate forms (Origin 

 of Species, Ed. VI., p. 338). My own views are fully explained in 

 Chapter XX I II. of my Island Life, published in 1880. I quite accept all 

 that Darwin, Hooker, and Asa Gray have written about the effect of the 

 Glacial epoch in bringing about the present distribution of alpine and 

 arctic plants in the northern hemisphere." Note by Mr. Wallace. 



3 The affinity with the flora of the Eastern African islands was long 

 ago pointed out by Sir J. D. Hooker, Linn. Soc. Journal, VI., 1861, p. 3. 

 Speaking of the plants of Clarence Peak in Fernando Po, he says, " The 

 next affinity is with Mauritius, Bourbon, and Madagascar : of the whole 76 

 species, 16 inhabit these places and 8 more are closely allied to plants 

 from there. Three temperate species are peculiar to Clarence Peak and 

 the East African islands. . . . " The facts to which Mr. Wallace called 

 Darwin's attention are given by Mr. J. G. Baker in Nature, Dec. gth, 1880, 

 p. 125. He mentions the Madagascar Viola, which occurs elsewhere only 

 at 7,000 ft. in the Cameroons, at 10,000 ft. in Fernando Po and in the 

 Abyssinian mountains ; and the same thing is true of the Madagascar 

 Geranium. In Mr. Wallace's letter to Darwin, dated Jan. ist, 1881, he 

 evidently uses the expression "passing through the air" in contradis- 

 tinction to the migration of a species by gradual extension of its area 

 on land. " Through the air " would moreover include occasional modes 

 of transport other than simple carriage by wind : eg., the seeds might 

 be carried by birds, either attached to the feathers or to the mud on their 

 feet, or in their crops or intestines. 



