Vol. XXXI. Part 7. JULY 2. 1920, 



Agricultural Gazette of New South Wales. 



Natural Crossing in Wheat* 



J. T. PRIDHAM, Plant Breeder. 



Darwin, in his " Variation of Animals and Plants," says " the flowering 

 structures of all plants are so arranged, that we may conclude . . that 

 the capacity for occasionally intercrossing is present or has been formerly 

 present with all plants." On the same subject, De Vries remarks : " It was 

 assumed that crosses were of common occurrence only with rye, the other 

 grains fertilising themselves ; but experience has shown that this is only an 

 average rule, and that everywhere, in the field, accidental crosses may 

 occur." O. F. Cook has pointed out that " natui-al crossing is common 

 among cultivated wheats in Palestine, In addition to a full series of 

 different forms of heads . . there is an equally complete range in colour." 



The Howards, in India, state that "231 cases were proved by us at 

 Lyallpur, and of these no less than 226 took place in 1907. In the dry 

 climate of the Chenab colony, wheat is grown entirely by eanal irrigation 

 and is usually watered at least twice after sowing, the last w'atering taking 

 place after the plants are in ear. Often before this last watering, the soil 

 moisture is so small that the plants wilt during the hottest part of the day, 

 the glumes open and the stigmas are exposed. Natural crossing is thus easy 

 and it is not surprising that it is so frequent." H. Pye, of Victoria, in 1914 

 wrote: " I am beginning to find more natural crosses than ever . . I 

 think the anthers are deficient in pollen or shrivel, and the ear opens for 

 wind infection." 



On the other hand, Garton, of England, considered from his emasculating 

 experin>ents that natural crossing did not exist. Bifien, of Cambridge, after 

 growing over 200 varieties, says : " I have never met with a case." 



Although natural crosses are very rare in the damp climate of England, 

 it is otherwise in the drier and more sunny latitudes. Koernicke, at 

 Popplesdorf, records several cases and says that Triticum compactum is more 

 disposed than any other form to cross in the field. Hansen, at Lyngby, and 

 Nilsson, at Svalof, find that in warm, good weather forms that are generally 

 considered self -fertilised cross with each other, and that crossing between 

 common wheats and spelts occurs under such circumstances. Mr. Pye also 

 finds these forms most prone to the phenomenon. 



Rimpau says, " During thirty-five years, thirty varieties of wheat were 

 grown near one another, and only twelve cases of cross-fertilisation were 

 noted ; fifty kinds of barley were cultivated in close proximity for twenty- 

 five years, bat only nineteen cases occurred." 



H. K. Hays, of Minnesota, in. giving his I'ecent experience says : — 

 " Results show that in 1917 there was considerable natural crossing — quite 

 2 to 3 per- cent. Crossbreds made many years ago, and now comparatively 



A 



