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 
F, 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 F; 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 F; 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 F, 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 
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