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RUL/LETIN 1134, IT. S. DEPARTMENT OF AGRICULTURE. 



The results of this experiment are exceptional, practically the same 

 total percentage of vicinists having been yielded by seed from the 

 Egyptian and from the upland plants, and the percentage yielded by 

 seed from the row of each variety which was most distant from the 

 plat of the other type (row 7) having been not significantly lower 

 than that yielded by the row that was nearest (row 1). 



Seed was gathered in 1920 from each of a number of rows in a 

 field of Pima (Egyptian) cotton at Buckeye, Ariz., which was sepa- 

 rated from a field of upland cotton by a rather wide road bordered 

 by a row of trees. Each lot of seed was thoroughly mixed, and a 

 portion of that from each row was planted in 1921 in order to deter- 

 mine the percentages of vicinists. No thinning was done, all seeds 

 which germinated having been allowed to develop. The results are 

 stated in Table 4. 



Table 4. — Vicinists yielded in 1921 by plantings of seed collected in 1920 from 

 several rows of Pima cotton situated in close proximity to a field of upland 

 cotton at Buckeye, Ariz. 



[No. 1 designates the outside 



row, nearest the upland field.] 









Plants. 



Fi hybrids. 



Row. 



Plants. 



Fi hybrids. 



Row. 



Num- 

 ber. 



Per cent. 



Num- 

 ber. 



Percent. 



No.l 



284 

 314 

 305 

 287 

 291 

 189 



6 

 2 

 1 



4 

 

 



2.1 

 .6 

 .3 



1.4 











No. 20 



143 

 138 

 136 



285 



1 



1 

 3 

 5 



0.7 



No. 2 



No. 30 ... 



.7 



No. 3 



No. 40 



2.2 





No. 50 



1.8 



No 10 



Total 





No. 15 



2,372 



23 



1.0 









It is interesting to note that the most distant row (No. 50) yielded 

 a percentage of vicinists not materially lower than that yielded 

 b}' row No. 1, which was nearest the field of upland cotton. It seems, 

 however, that pollinating insects which had left one field and crossed 

 a wide road bordered by trees would be as likely to alight at a con- 

 siderable distance within the second field as at the edge of it. 



VICINISM BETWEEN VARIETIES OF THE SAME TYPE. 



The cases of vicinism in Arizona thus far discussed have been 

 between widely different types of cotton. It will be interesting to 

 consider a case involving two related varieties belonging to the 

 same general type but sufficiently uniform and sufficiently distinct 

 to make the recognition of accidental hybrids between them fairty 

 certain. A row of Pima cotton was grown side by side with a 

 row of Gila cotton, both varieties belonging to the Egyptian type, 7 

 at Sacaton, Ariz., in 1916. In this case there was no appreciable 

 difference in the height of the plants and the duration of the flower- 

 ing period. Seed from the open-pollinated Pima flowers was 

 planted in 1917. The hills were thinned to one plant, the thinning 

 having been done in such manner as to avoid selection. The total 

 number of plants after thinning was 302, of which 5 were certainly 

 and 2 more were doubtful first-generation Pima X Gila hybrids. The 



7 These varieties are described by Kearney (27), and the characters of hybrids be- 

 tween them are discussed by Kearney and Wells (30). 



