, FIELD CROPS. 839 



duced an average gain per acre over Zimmer Spanish of 428 lbs,, or 43.9 per 

 cent, and 482 lbs., or 52.1 per cent, respectively. 



Experiments with the Cuban variety indicated that considerable improve- 

 ment in yield and in the reduction of suckers is possible through selection. By 

 this means, the yield was increased from slightly over one-half to more than 

 three-fourths of the yield of Zimmer Spanish. As the yielding capacity of the 

 variety is so low, no practical results were obtained. Under the conditions 

 existing in the Miami Valley district, this variety undergoes a marked breaking 

 up in type, but the range in variation was not found so great as in hybrids 

 between radically different varieties. 



Hybridization work was begun at Germantown in 1903 by making 26 distinct 

 crosses between Connecticut Seedleaf and Cuban varieties. In 1904, crosses 

 were made between these first hybrids and Ohio Seedleaf and Zimmer Spanish, 

 together with one each between Zimmer Spanish and Ohio Seedleaf and Zimmer 

 Spanish and Cuban. The next year a large number of crosses were made be- 

 tween Cuban, Zimmer Spanish, Ohio Seedleaf, and several hybrids already 

 made in divers combinations. Since that time, new hybrids have been made 

 each year, among them a number whose parents were both of Seedleaf type. 



The hybrids are arranged in 4 groups of which the first includes the Havana 

 or Spanish types, more or less closely approaching Zimmer Spanish, the second 

 contains the Seedleaf class, the third those intermediate between Seedleaf and 

 Spanish, and the fourth the Cuban and Connecticut Seedleaf hybrids. Of the 

 26 hybrids between Cuban and Connecticut Seedleaf made in 1903, only 5 were 

 retained as worthy of propagation. The variation in this lot of hybrids was 

 extreme, and in the second generation it was so great that no 2 plants of suffi- 

 cient individual merit to warrant propagation bore any considerable resemblance 

 to each other. 



The individual annual records of the important members of each group of 

 hybrids are summarized in tables. A comparison of yields of 24 hybrids and 8 

 varieties presented a general increase in the relative yields of the hybrids 

 during the 3 years 1908-1910. The average increase per acre ove^ Zimmer 

 Spanish for all hybrids in 1908 was 189 lbs., in 1909 227 lbs., and in 1910 

 405 lbs. 



Experiments to determine the possibility of growing tobacco ci'ops as first- 

 generation hybrids were carried on during several seasons. Zimmer Spanish 

 was selected for determining the effects of cross-fertilization within the limits 

 of a fixed variety. The average of all results gave a gain of only about 25 

 lbs. per acre in favor of cross-fertilization. The lack of variation in Zimmer 

 Spanish, or its fixity of type, is giA-en as a possible explanation of this result. 

 In 1907, pairs of plants of distinct varieties were selected and 2 lots of seed 

 from each plant, one arising from self and the other from cross-fertilization, 

 were secured. The results of this seed from 8 plantings for each pair of parent 

 plants showed that in all cases the hybrids exceeded in yield not only the 

 average of their parents but also their more productive parents. The minimum 

 increase per acre was 67 lbs., while the maximum was 285 lbs., and the average 

 165 lbs. In 1909, 39 new hybrids were tested in a similar way with their 

 parent plants. These hybrids, in most cases produced considerably more than 

 the parental average, but a number of them failed to reach the yield made by 

 the more productive parent. This year the hybrid yields ranged from a mini- 

 mum of a decrease per acre of 160 lbs. to a maximum of an increase of 492 

 lbs., the average of the hybrids being about 185 lbs. greater per acre than that of 

 their parent plants. In discussing the relation of parental yields to that of hybrids, 

 the authors state that in many instances they have been able to produce in the 

 third and later generations yields much in excess of the yield of the first gen- 

 70257°— No. 9—13 4 



