EXPERIMENTAL EVOLUTION 155 
ing them is not too great, it is a distinct advantage to move a number of 
individuals in the same block of earth. The transfer of mature plants is 
inadvisable, except for those perennials which can not readily be secured in 
an early stage. This naturally does not apply to woody -plants, evergreen 
herbs, mosses and lichens ; the last two may be transferred at any time with 
satisfactory results. Each culture is carefully marked with stakes, and 
definitely located by means of landmarks. 
Fig. 46. Series for producing hydrophytic forms under control: 
1, amphibious; 2, floating; 3, competition; 4, submerged. 
Reciprocal transiers may be made by means of seed or plant. Since the 
experiment is a complex one, all the care possible should be taken to make 
sure that the plants become established in the reciprocal situations, and con- 
sequently, it is often advisable to transfer both seeds and plants. Reciprocal 
transfer is of paramount value in solving the problem which bog plants 
present. A slight modification of the method makes it possible to obtain 
experimental evidence of the polyphyletic origin of species in consequence 
of adaptation. In an experiment mentioned elsewhere, the transfer of 
Kuhnistera purpurea to the area occupied by K. candida, and vice versa, is 
designed to show whether ‘one has been derived from the other. If the two 
species are moved into an area which contains more water than that usually 
occupied by K. purpurea, and less water than is found where K. candida 
habitually grows, the resulting modifications will throw much light upon the 
