UTILIZATION OF HYBRIDS IN PLANT BREEDING 363 



having been isolated, they can be maintained and the crosses may be 

 repeated from time to time. This is a very important consideration for 

 the grower who wishes to put the same grade of product on the market 

 from year to year. "As tomato seed remains fertile from 3 to 7 years, 

 a grower does not need to make his crosses oftener than once in 

 3 years. The seedsman, as well as the farmer, can profitably raise 

 FI generation seed, provided a guarantee is not given for more than one 

 generation, for the buyer, to maintain his quality of product, will have to 

 purchase seed every year." Wellington thinks the best results with 

 tomatoes can be obtained by keeping within a species and crossing 

 distinct varieties or strains. Dominant characters, that will certainly 

 appear in the fruits of FI plants if present in either parent are rough or 

 irregular shape, dark red color as contrasted with pink or yellow and 

 pink as contrasted with yellow. Size and season of ripening in Fi will 

 be intermediate between the parental characters. 



Jones and Hayes report results of similar experiments which corrobo- 

 rate Wellington's conclusions. Of two different crosses one (Stone x 

 Dwarf Champion) gave an appreciable increase in both size and number 

 of fruits and the total yield was thereby increased. It even exceeded 

 the better parent by 15 per cent. Moreover, the increase above the latter 

 parent was uniform throughout the four years of the test. The other 

 cross (Lorillard x Best of All) exceeded slightly the better parent in 

 average weight of fruit but it did not excel in total yield. "These re- 

 sults show that not all combinations of tomato varieties give the vigor 

 usually derived from crossing, but when a desirable combination is found 

 it can be counted on to give the increase in yield every time the cross is 

 made. Vigor due to crossing as measured by increased yield was not 

 appreciably greater in crosses between artificially selfed strains than 

 in crosses between ordinary commercial varieties. These results are in 

 agreement with the fact that the tomato is naturally almost completely 

 self-fertilized. The cross of Stone x Dwarf Champion which gave a 

 significant increase in yield also showed a hastening of the time of pro- 

 duction. It not only gave a 15 per cent, larger yield than the later 

 parental variety but was earlier in its time of production than the earlier 

 parent. Hence its value to market gardeners was increased." 



Similarly, in tobacco, Selby and Houser claim that the culture of first- 

 generation hybrids will prove both profitable and practicable. Since the 

 added cost of producing hybrid seed should not exceed 50 cents per acre 

 and the crossing need not be repeated oftener than once in 3 years, 

 the financial consideration is negligible. In regard to uniformity of crop 

 they find that FI hybrids between pure varieties or fixed hybrids show no 

 essential difference in uniformity from the parent varieties and for com- 

 mercial purposes only such parents should be used. As for yield their 



