INTRODUCTION. 21 



undergone definite adaptation to the controlling factor and have become ecads. In 

 cases where the migration is interrupted, the question of descent lacks the final degree 

 of certainty where more than one parent species may be concerned. In mountain regions 

 where the topography is rugged and rapidly changing, habitats are so fragmented that 

 they recur again and again in the same relation to each other. This offers ideal conditions 

 for the invasion of new habitats, and the ecads of plastic species occur repeatedly. In 

 many cases, gravity is the migration agent, and in others the annual extension of root- 

 stock or runner brings about invasion. In both instances there is not only complete 

 continuity in space, but often also in time, so that the question of the .specific stock from 

 which the ecad has sprung is as certain as in experiments started artificially. 



Artificial experiments differ from natural ones chiefly in that the question of origin 

 is always a matter of certainty. They differ also in being carried on necessarily under 

 control, owing to the fact that the number of individuals is limited, and no chances can 

 be taken with their loss. In nature there may be a hundred or a thousand individuals 

 of an ecad in one spot, and this may occur repeatedly in a restricted mountain region. 

 Thus, while it is sometimes desirable to protect a particular group from rodents, for 

 example, it is rarely necessary. In artificial experiments, control and natural conditions 

 are often antagonistic, and the decision between them must be made upon the basis of 

 the results desired. In the case of hybridization this difficulty does not exist, since 

 physical factors are not taken into account, and investigations of this process are espe- 

 cially adapted to garden and greenhouse. On the other hand, the origin and differen- 

 tiation of existing species and ecads can best be studied in the field, as garden and 

 greenhouse conditions can only be made to approximate natural habitats at the best. 

 However, the plasticity of species and their reaction to known factors furnish admirable 

 subjects for study under complete control, and certain aspects of mutation are also best 

 studied in this manner. 



In experiments at the Alpine Laboratory, where the chance of disturbance by man 

 is slight, the degree of control has varied. Grasses and cacti require little protection in 

 a region without grazing, and the garden of plains species has not been fenced. In the 

 case of reciprocal transplants, it has not seemed practicable to protect each scattered 

 individual with wire netting. With alpine plants, however, their early appearance and 

 succulence, as well as the labor involved in transplanting, has made it necessary to fence 

 the gardens against rodents from the first. This involves practically no change of the 

 physical factors, if plants are kept away from the sides of the fence toward the sun, 

 and the experience of several years indicates that all transplants and other field experi- 

 ments can well be fenced, except in the case of natural experiments involving many 

 individuals. The hazards of weather, such as hail and flood, alone work suflficient 

 damage, and against these there is no protection that does not change conditions. The 

 fencing of reciprocal transplants requires especial care to see that the plant is at no times 

 shaded by the netting or harmed by the wind. Finally, adequate control in the case 

 of transplants requires the reduction or elimination of competition where they are 

 planted into other communities, since this involves a factor not readily measured. 



Method of experiment — The primary methods of experiment in the field are trans- 

 planting, planting, seeding, and modification of the habitat. The details of these methods 

 belong in another place, and it will suffice here to point out their differences and values. 

 Transplanting consists in transferring the adult plant from one climate, habitat, or 

 situation to another. It is reciprocal when two related species, a species and its variad, 

 or two related variads are concerned. Climatic transplants are those in which a species 

 is transferred from one climate or subclimate to another or to more than one, as when 

 alpine species are moved to the montane and plains region, or a dominant of the true 

 prairie to the mixed prairie and the bunch-grass prairie. Habitat or edaphic transplants 



