VARIATION 355 



of the plants. Without at present being able to offer any explanation of 

 the processes involved, I am inclined to look upon them as the product 

 of hybrids, the ordinary segregation of which has been delayed or in- 

 hibited for a time. 



The various races of wheat differ considerably in their tendency to 

 sport or mutate ; those in which evidence points to their being of hybrid 

 ancestry are much more subject to this kind of variation than the purer 

 races. For example, sports are much more frequent in T. vulgare and 

 T. compactum, two races which I regard as hybrid (pp. 342, 346), than in 

 T. durum or T. dicoccum. I have never seen an example in T. monococcum, 

 the race which gives no fertile hybrids. Certain forms, such as the Square- 

 head vulgare wheats, are also especially liable to vary in this manner. 

 Changes in the environment appear to stimulate the production of sports. 

 In some seasons, especially those with an abnormally high average summer 

 temperature following severe winters, sports arc more frequent than usual 

 in autumn-sown wheat. Rimpau records great variation among Square- 

 head wheats throughout Germany in 1903, especially among the bearded 

 forms which had before been very constant and pure. 



Buthiin obtained sports in Black Hmmer and a Turkey Red type of 

 vulgare wheat immediately after sowing in rich " sagebrush " soil at an 

 altitude of 4000 feet in Wyoming. 



SPELTOID MUTATIONS. These sports observed among the descendants 

 of pedigree cultures and hybrids of T. vulgare have the narrow open ears 

 and truncate empty glumes of T. Spelta ; the culms arc tall and the ears 

 erect, rigid, and harsh. 



Most of them are heterozygotcs, which segregate into homozygote 

 normal forms and heterozygotc spcltoids in the ratio I : I, which Nilsson- 

 Ehle explains by the assumption of the total elimination of male spcltoid 

 gametes. 



In a few cases segregation occurs into normal forms, heterozygous 

 speltoids and homozygoiu spcltoids in the ratio I : 2 : i, but more often 

 the proportion of speltoid forms is smaller than this owing to the partial 

 failure of male gametes. 



I have found considerable numbers of speltoid forms (2, Fig. 173) 

 among mixed samples of vulgare wheats from Persia, Central Asia, Spain, 

 and Argentina ; these, however, are usually homo/ygous. 



DWARFS.- Dwarf plants with short culms and compact short ears 

 are tound in the F a and subsequent generations of hybrids of certain 

 races of wheats. Some of them are fertile, with normal glumes and 

 grain ; others are monstrous forms with deformed sterile ears. 



I have never observed the production of dwarf mutants among pedigree 

 lines of wheats, nor have I met with clear references to am. Farrer, 



