142 BULLETIN 623, IT. S. DEPARTMENT OF AGRICULTURE. 



have been used almost universally for this purpose. This practice 

 has led to the propagation of a continually increasing proportion of 

 trees of those strains producing the largest amount of sucker growth. 

 Inasmuch as such trees are usually light bearers and produce inferior 

 fruits, this practice has been unfortunate and is the direct cause of the 

 presence of the large proportion of unproductive trees found in many 

 orchards. In cases where fruit wood has been used for propagation, 

 such bud wood has been cut without any fruits attached, so that in 

 many instances buds from sporting limbs have been used, resulting 

 in the development of diverse strains of trees, as shown by the presence 

 of such trees in the established orchards. 



The well-known condition of frequent mixture of varieties in 

 deciduous orchards, resulting from the use of bud wood cut from young 

 nursery trees, where buds from different varieties are likely to be 

 mixed or misplaced during propagation, caused the California 

 citrus nurserymen largely to avoid this practice. For this reason 

 only a limited amount of nursery growth has been used for propa- 

 gation, and consequently but little mixture of varieties has been 

 ■found in Washington Navel orange orchards. 



The presence in established orchards of trees of diverse strains is 

 the direct result of propagating either from individual trees of these 

 strains or from limb variations in trees of the Washington strain. 

 Because this condition of bud variation and strain diversity was 

 practically unknown until established through these investigations, the 

 nurserymen who used bud wood accidentally cut from the sporting 

 branches of trees of the Washington strain (see figs. 7 and 8) or even 

 bud wood from trees of inferior strains are not to blame for the propa- 

 gation of these diverse and frequently undesirable strains. However, 

 now that the condition of bud variability in the trees of this variety 

 has been established beyond question, any propagator who does 

 not utilize this information and practice the improved methods for 

 securing bud wood from select trees of the best strains will not be 

 able to excuse the poor results of his propagations on the ground 

 of the lack of definite information on this subject. 



THE ISOLATION OF STRAINS THROUGH BUD SELECTION. 



Fruit-bearing bud wood has been selected from limb variations 

 occurring in trees of the Washington or other strains, and in several 

 hundred cases where the growth from these buds has fruited every 

 selection has come true. In the beginning of this work, the con- 

 spicuous bud variations were top-worked in bearing trees in order 

 to get them in fruiting quickly. Later, as opportunity has per- 

 mitted, the bud variations have been propagated on nursery stocks. 

 Naturally, the results of these progeny tests require considerable 

 time in order to secure reliable' performance-record data. In so 



