412 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



II. 



For the first 20 or 30 years after the appearance of the Origin 

 of Species research was chiefly directed to the study of the direct 

 action of environment as it works in free nature and is made to 

 work in our experiments. The chief result of these researches was 

 to prove, first, that there are no such specific characters, either in 

 plants or in animals, as could not be altered by modifying their 

 physical conditions of life ; and, second, that the variations obtained 

 experimentally under certain conditions of heat or cold, dryness or 

 moisture, rich or poor nutrition, and so on, were exactly those which 

 are characteristic for animals and plants living in the Arctic and 

 the Torrid Zone, in a dry and in a wet climate, in fertile prairies 

 and in deserts. It was thus proved that if a species of plants or 

 animals migrated from a warmer into a cooler region, or from the 

 seacoast inland, or from a prairie land into a desert, variation itself 

 amongst the new immigrants, apart from natural selection, would 

 tend to create a variety representing an adaptation to the new con- 

 ditions. The same would happen if the climate of a given locality 

 underwent a change for some physiographical reason. In both cases 

 natural selection would thus play a quite subordinate part — that of 

 a "handmaid to variation," as Hooker wrote in one of his letters 

 to Darwin. It would have only to weed out the weaklings — those 

 who would not possess the necessary plasticity for undergoing the 

 necessary changes in their tissues, their organs, and (with animals) 

 in their habits. 



The researches of those years having shown how the floras and 

 the faunas of the Arctic barren lands, the Alpine summits, the Afri- 

 can swamps, the seacoasts, the deserts, and the steppes were adapted 

 to withstand the climate and the general conditions of life in each 

 of these surroundings, the first steps were also made, especially by 

 botanists, to prove that most of these wonderful adaptations could 

 be reproduced in a short time in our experiments. It was sufficient 

 for that to rear the plants or the animals in those conditions of 

 temperature, moisture, light, nourishment, and so on, which prevail 

 in the different regions of the earth. Hence, already then, especially 

 for those who were acquainted with nature itself, it appeared most 

 improbable that the adaptations of plants and animals which we 

 see in nature should be the results of merely accidental, fortuitous 

 variations. 



To take one of the simplest instances — we had learned from ex- 

 periments that when a plant was grown under a glass bell in a very 

 dry air its leaves soon ceased to develop succulent lobes, and the 

 ribs of the leaves were turned into spines or prickles. And when 

 we saw that spiny plants were characteristic of the vegetation of 



