164 Gigantism in Primula sinensis 



dominant to the normal form. Thus, as de Vries {op. dt.) has shown, 

 Oenothera gigas, a giant mutant from 0. Lamarckiana, when crossed 

 with the latter form (0. Lamarckiana x 0. gigas) yields an F^ consisting 

 of plants all possessing giant characters. In both Lathyrus odoratus 

 and Pisum sativum the character of gigantism is known to be deter- 

 mined by two factors, the presence of both of which is necessary for 

 the manifestation of the character. 



The purpose of the present communication is to record the 

 origination of a giant form of P. sinensis from a normal form the 

 pedigree of which is known, to describe the histological characteristics 

 which distinguish this giant, to present the results of the experiments 

 which have been made on the genetics of gigantism and to discuss 

 a few of the problems which are suggested by the results of these 

 experiments. 



II. Gigantism in Primula sinensis. 



x^mong the many varieties of Primula sinensis in cultivation at 

 the present day there are not a few which are characterised by an 

 imposing massiveness of both floral and vegetative organs. The races 

 thus distinguished are known to florists as giants and are prized by 

 them on account of the remarkable size and substantiality of their 

 flowers. Associated with the gigantic habit are a somewhat slow rate 

 of growth, a certain leisureliness of flowering, and, not infrequently 

 a considerable measure of infertility. It is probable that the last 

 mentioned characteristic accounts for the opinion, not uncommon 

 among gardeners, that giants are more difficult of cultivation than 

 are the normal races. This opinion, however, is not well founded, 

 nor is there any ground for the assertion, which is often made, that 

 the gigantism of these strains depends on methods of cultivation. 

 The fact that seedsmen are able to offer giant races year after year 

 i^ well nigh sufficient evidence that gigantism is a " fixed " character, 

 and that giants, when self-fertilized, breed true to form. 



Beyond these facts little is known either of the origin of the 

 giant races of P. sinensis {cf. Gregory 1909 and 1911) or of their 

 genetical behaviour. The physiological peculiarities of giants are 

 likewise unknown. 



The giant races of P. sinensis which are offered by seedsmen are 

 almost invariably of the sinensis type both with respect to habit and 

 flower: that is to say the flowers are produced in a compact and 



