168 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



these trees represent all sorts of relationships and degrees, a few being 

 first crosses, but many more being of the second, third or even later gen- 

 erations. Of the trees tested by ourselves and by a few of the most 

 progressive nurserymen who have taken the trouble to plant the nuts 

 from various trees separately, only an extremely small proportion have 

 shown themselves worthy of being used for producing rootstocks for the 

 English walnut. To test such a tree thoroughly requires several years, 

 inasmuch as the nuts must first be planted and the seedlings raised to 

 grafting age, the trees then grafted and kept in the nursery for at least 

 another year, after which they must be planted out in various types of 

 soil and their growth observed for some time in comparison with that of 

 trees on other roots. The majority of hybrid trees which produce seed- 

 lings of exceptional vigor among their progeny do this in an extremely 

 irregular manner, the seedlings being of all sorts of sizes and char- 

 acteristics. English walnuts grafted on such seedlings will vary corre- 

 spondingly. As we have previously said, no Paradox trees have been 

 found whose seedlings are desirable as rootstocks, and of all the Royal 

 trees which have been tested there are less than half a dozen in the State 

 at present ^whose seedlings are known to be of sufficient uniformity in 

 good qualities to be desirable for propagation. Seedlings of most Royal 

 hybrids are really inferior to those of the straight California black 

 walnut of either species for nursery purposes on account of their lack of 

 uniformity. At least one nurseryman in the State is taking the trouble 

 to hybridize certain black walnut trees by hand in order to obtain a 

 walnut cross which he considers especially desirable for the nursery. 



One fact is to be remembered in connection with the progeny of any 

 California walnut tree, namely, that in almost every instance walnut 

 trees of some sort stand near to each other, and cross-pollination is there- 

 fore always possible and probably always goes on in every instance to a 

 greater or less extent. The tree therefore which gives an unusually good 

 lot of seedlings might not do the same at all if it stood elsewhere, removed 

 from certain other trees which stand near it and which cross-pollinate its 

 blossoms. It is therefore also true that it may or may not always be 

 possible to perpetuate a desirable tree of this sort even by grafting, since 

 when planted in some other place the combination of cross-pollination 

 which resulted in the production of exceptionally good seedlings may be 

 entirely lost. 



FREAK WALNUT TREES. 



Walnut trees are quite frequently met with in California which, while 

 it is probable that they are mostly hybrids, present very peculiar char- 

 acteristics and have little resemblance to any known species. It is pos- 

 sible that these may be partly the effect of environment as well as that 

 of hybridization. About the city of Berkeley there are a number of 



