276 Vniversitfi of California Publicat ion.s in Agriciill nr<il Sciences [Vol. ti 



and garden. The number of different forms resulting either in the 

 first or later generations and as a result of controlled cross-pollinations 

 show that the germinal material was indeed far from homozygous. 

 It is of importance, because of some current theories regarding the 

 influence of the habitat upon the genotype of a local species (Tures- 

 son, 1922), to observe the behavior of these various forms when grown 

 in as nearly identical conditions as can ordinarily be furnished in a 

 greenhouse or garden. Plants belonging to many different genera 

 were collected by Turesson from contrasted habitat localities in 

 Sweden and grown together in a common garden. He found that 

 in general each particular type of a species found in each of several 

 different habitats maintained its characteristics in the absence of the 

 habitat to which it seemed especially modified. He sees in such 

 phenomena a refutation of the theory, now generally held, that the 

 form predominating in a given locality occurred as a chance mutation 

 or recombination and was preserved through natural selection. The 

 theory substituted for this is Lamarckianism expressed in modern 

 terminology, namely, habitat causes a change in the fundamental 

 genotype of the species such that a phenotype is developed which 

 permits the plant to flourish in a specialized habitat. His report 

 deals principally with three types of plants in all his species, viz., 

 dwarf forms, upright or erect forms, and spreading or procumbent 

 forms, each of which was found in a location favorable to the existence 

 of that type while unfavorable to the other types; and each thus 

 becomes a demonstration of the effects of natural selection. In our 

 study of Crepis forms we have not been fortunate enough to study 

 wild populations of Crcjyis in all of the localities from which we have 

 obtained seed, but we have produced hereditary strains of erect forms, 

 spreading forms, and dwarf forms from the same habitat at Eureka, 

 a fact which does not especially favor the existence of any one type. 

 Dwarf forms have also appeared in cultures from other places (France 

 and Denmark), whose definite habitat characteristics are unknown 

 to us. Similar plant forms are well known to occur sporadically in 

 many wild and domesticated species. Mutations giving rise to pros- 

 trate and dwarf types in plants are not infrequent when compared 

 to other types of change. If we accept the idea of a gcnotypic response 

 of the species to the habitat, are we not also admitting the inconstancy 

 of the gene, a theory which is no longer tenable? Continuing the 

 assumption, it is not clear why these different hereditary types, such 

 as we have in Crepis, remain constant in a single unvarying habitat. 



