210 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



rather than a matter of any general rules applying to all crosses between 

 certain species. 



Royal Hybrid Roots. Here again we enter the domain of the special- 

 ist rather than that of the average, commercial nurseryman. We have 

 stated elsewhere that in the Royal hybrid (the cross between California 

 and eastern black walnuts) many very thrifty, vigorous trees occur 

 and that this vigor is carried over into the second generation much 

 more than in the Paradox. In other words, experience has shown that 

 while seedlings from Paradox trees do not have the exceptional vigor 

 of the parents, there are some first-generation Royal trees which 

 transmit their exceptional rapidity of growth to their progeny of the 

 second generation. These trees vary greatly, however, in regard to 

 the character of their seedlings and it is only a very few which produce 

 nuts that give a uniform lot of seedlings as good as the parent. Such 

 trees, when found and thoroughly tested, are extremely valuable. We 

 wish again to emphasize the fact, however, that indiscriminate plant- 

 ing of nuts from Royal hybrid trees cannot be expected to give 

 uniformly good seedlings for grafting purposes but rather will result 

 in a most heterogeneous mixture of trees of all sizes, characteristics 

 and degrees of vigor. The Royal trees found growing about the State 

 are of various generations^ many of them of the second generation, 

 of which the seedlings are decidedly inferior, and the nurserymen 

 would do better to plant the nuts of the straight northern or southern 

 California black walnut than to pick up Royal nuts at random. The 

 propagation of English walnuts on the Royal root with the idea of 

 getting trees of marked superiority over those grown on the California 

 species is again, as in the case of the Paradox, the work of the specialist 

 who is disposed to try out individual trees carefully as to the nature 

 of the seedlings and that of trees grafted upon them, a process which 

 takes several years in the case of each individual Royal tree thus 

 tested. Trees of real excellence upon this root must also, therefore, be 

 grown by the specialist and command a considerably higher price 

 than ordinary trees. It should be equally understood that really select 

 trees on these exceptional roots constitute the very acme of perfection 

 in walnut trees as to vigor and hardiness, that they can be produced 

 only by the exceptional nurserymen and probably they will be purchased 

 only by growers who are willing to pay a premium in order to obtain 

 an exceptional orchard. Trees upon well-grown roots of either of 

 the ordinary California species are thoroughly good and first class, and 

 need not be deprecated on account of the fact that it is possible to grow 

 these exceptional trees to a limited extent on properly selected and 

 tested hybrid roots. Indiscriminate trees of the latter class, it should 

 also be understood, are no better than and perhaps inferior to those of 



