328 



The Journal of Heredity 



ural crossini^ in wheat was more com- 

 niun in the Northwest than had for- 

 p.ierlv been supposed to be the case, or 

 that the seasons of 1915 and 1916 were 

 very favorable for cross polHnation.* 

 The results here reported show that in 

 1917 there was also considerable natural 

 crossings;. 



The i)lan has been followed of grow- 

 ing a purity plot of 50 to 100 plants each 

 vear of those selections and crosses 

 which are being tested for yield in the 

 rod rows. In these purity plots each 

 plant is individually spaced and each 

 plot is grown from a single plant se- 

 lected at random from the previous 

 year's purity plot. 



In 1917 rows of Haynes Bluestem, an 

 awnless. hairy chaffed wheat, were 

 grown alternately with the purity plots. 

 Individual plants for 1918 planting 

 were selected in each purity row as 

 usual. In 1918 these purity rows were 

 carefully examined, and those crosses 

 which ''ould be determined were noted. 

 The number of such crosses is given in 

 the table in the appendix (page 334). 



Aside from these, which were grown 

 near Bluestem the preceding year, there 

 were 49 other spring wheat plots 

 grown from individual plants. Four 

 thousand was the approximate number 

 of plants examined in these 49 plots. 

 Nineteen plants, which were F^ crosses 

 were observed. The rod row plots were 

 also examined in both the spring and 

 winter wheat nurseries. No crosses were 

 noted in the durum rows, of which 24 

 were grown. Approximately 400 rod 

 rows of spring wheat (T. vulgarc) 

 were examined, and 52 plants were 

 found which were believed to be the 

 result of natural crosses. Only such 

 crosses as could be accurately deter- 

 mined were counted. 



In the winter wheat nursery the ])ur- 

 ity rows were almost entirely winter 

 killed. F.etween 600 and 800 rod rows 

 were examined, and over 100 plants 

 were observed which were believed to 



be b, crosses. Many absolutely clear 

 cases were found ; for example, plants 

 with intermediate awns in bearded va- 

 rieties belonging to the Crimean group. 

 A number of such ])lants were found in 

 rows of Turkey pure-line varieties ob- 

 tained from Mr. Burnett, of the Ames 

 Fxperiment Station. The crosses were 

 noted the second season that they were 

 grown at University Farm. 



Observed crosses in Triticum vulgare 

 lines average 1.3%, and the conclusion 

 is certainly reasonable that cross polli- 

 nation occurred as often between plants 

 of the same variety as between ditferent 

 sorts. This would mean that natural 

 crossing in 1917 was at least 2% to 3%. 



NATURAL CROSSES AS A DIFFICULTY IN 

 PURIFYING HYBRIDS 



Among the sorts which have been 

 tested for yield in the spring-wheat nur- 

 sery are several crosses between Turkey 

 (winter) and a Fife variety. These 

 crosses were made many years ago, and 

 are now comparatively pure. In 1915 

 some hairy chaffed intermediate awned 

 wheats were noted in the rod rows of 

 these crosses. An attempt was made to 

 rogue these out, and in 1916 several 

 ])lots of each of these sorts were grown 

 from individual plants. These all ap- 

 parently bred true, but when they were 

 again placed in rod rows in 1917 there 

 were again a few ofT-type plants, and 

 many of these were clearly F^ crosses. 

 Unless these had been carefully studied, 

 the natural conclusion would have been 

 that this wheat could not be bred true. 

 A few such F^ plants overlooked may 

 be a cause of much greater mixture the 

 following year. Results of this nature 

 are believed to be a logical explanation 

 of the cause for the belief of some 

 agronomists that hybrids frequently re- 

 vert to tyjx'. 



During the last few years a consider- 

 able number of commercial samples of 

 Preston. Haynes I>luestem, Minnesota 

 169, and Marquis have been examined. 

 The P)luestem and Preston samples were 



* Hayes, H. K., Natural Cross Pollination in Wheat. Jour. 

 8, 1916, pp. 209-227. 



■liner. Soc. Ayron., Vol. 



