4 BULLETIN 1134, U. S. DEPARTMENT OF AGRICULTURE. 



is given by Leake (35), by Kottur (34), and by Thadani (46). 

 Kottur states that at Dharwar when two pure strains, one having a 

 long leaf and the other a short leaf, were grown side by side, 6 per 

 cent of vicinists occurred in the progeny of the short-leaf strain. 



The distance to which pollen may be carried under natural con- 

 ditions is a subject of much practical importance. Shoemaker (43) 

 observed that where Triumph and Okra Leaf cottons were grown 2 

 rods apart, 4 a planting from the seed of the former yielded about 

 1 per cent of hybrids. This would indicate that a relatively slight 

 distance affords a fair degree of protection against cross-pollination. 



Balls (8, pp. 19, 123), in Egypt, found that whereas under or- 

 dinary field conditions the number of vicinists ranged from 5 to 10 

 per cent, in his breeding plat, where numerous different types of 

 cotton were grown in close proximity, the percentage rose to as 

 high as 50 or even 100. He observed that hybrids were occasionally 

 produced with Willett's Red Leaf when the plants of the latter 

 were 50 meters distant from the plants which produced the hybrid- 

 ized seed, with dozens of other cotton plants intervening. 



Ricks and Brown (1), in Mississippi, found that seed gathered 

 from plants of the Cleveland variety of upland cotton which were 

 situated in the middle of a 4-row plat of this variety, the plat being 

 separated by 10 rows of corn from a row of Willett's Red Leaf 

 cotton, produced 0.8 per cent of Cleveland X Red Leaf hybrids, as 

 compared with 4.9 per cent where the two varieties were grown in 

 adjacent rows and 18.5 per cent where they were grown in alternate 

 hills. 



EXPERIMENTS IN ARIZONA. 



VICINISM BETWEEN VERY DISTTNCT TYPES. 



A plat of cotton of the Egyptian type was grown by the writer 

 at Yuma, Ariz., in 1907 in close proximity to a plat of upland cot- 

 ton. Seed from the open-pollinated flowers of the Egyptian plants 

 was planted in 1908, and of the resulting population of approxi- 

 mately 3,000 individuals 8.2 per cent were hybrid. 



Under the direction of O. F. Cook, Egyptian and Kekchi (upland) 

 cottons were planted in alternate rows by Argyle McLachlan near 

 Yuma in 1909. The population grown in 1910 from the seed pro- 

 duced by the Kekchi plants contained 5 per cent of hybrids. 5 



Open-pollinated bolls were collected at Sacaton in 1919 from 

 three adjacent rows of cotton, there having been a row of Pima 

 (Egyptian), bordered on one side by a row of the Lone Star (up- 

 land) variety and on the other by a row of the Holdon (upland) 

 variety. The seed obtained from each row was planted in 1920, 

 and the percentages of first-generation hybrids were determined, as 

 given in Table 1. 



'Although the point is not mentioned in the work cited, Dr. Shoemaker has informed 

 the writer that to the best of his recollection there were several rows of Triumph cotton 

 between the plants of that variety from which seed was gathered and the row of Okra 

 Leaf cotton. 



5 Argyle McLachlan in letter to O. P. Cook, July 9. 1910. 



