- BULLETIN 815, U. S. DEPARTMENT OF AGRICULTURE. 
the various strains originating from bud variations; wo d:scever 
methods for isolating the best and eliminating the inferior strains 
through bud selection; to originate and introduce methods for 
replacing trees of inferior strains in established orchards through 
top-working or replanting; to introduce methods for securing reliable 
supphes of buds from superior performance-record trees for use by 
propagators; and to establish a system of individual-tree record 
keeping in commercial lemon orchards, in order to locate the desirable 
and undesirable trees. 
PLAN OF THE INVESTIGATIONS. 
These investigations have been carried on by means of individual- 
tree performance records, as in the case of the citrus varieties pre- 
viously studied. The term ‘‘performance record” is used to mean 
a systematic record for a period of several years of the yield and 
behavior of individual trees. This record includes notes of the 
amount, the commercial quality, and the variability and other 
important characteristics of the fruits produced by the individual 
trees. In the case of lemon trees, individual performance records 
for at least two consecutive and normal seasons on trees which have 
‘reached a full bearing age are considered necessary in order to 
determine the value of the trees for commercial fruit production. 
Similar records for at least four years are advisable, in order to fur- 
nish the basis for the selection of superior trees as sources of bud 
wood for propagation. 
The same general methods of picking, handling, assorting, weigh- _ 
ing, counting, and classifying the fruits that were described in detail 
in United States Department of Agriculture Bulletin 813, entitled 
“Citrus-Fruit Improvement: A Study of Bud Variation in the Eureka 
Lemon,’’ were followed in the studies of the Lisbon lemon. 
The conditions considered essential in the location of the Lisbon 
individual-tree performance-record plats were the same as those 
which determined the final location of similar record plats of other 
varieties, namely, (1) the production of successful and profitable 
crops of fruit; (2) location on virgin land in order to avoid any in- 
fluence of previous cultural treatment; (3) protection from cold, 
strong winds, or other climatic causes of tree and fruit injuries; (4) 
the absence of radical pruning, rebudding, top-working, or other 
similar tree treatments; (5) freedom from or the aficaae control of 
diseases and insect pests: (6) uniform irrigation and cultural practices 
during the entire history of the orchard; (7) reliable information con- 
cerning the history of the buds used in the propagation of the trees 
and the kind of stocks; (8) the prospect of settled ownership for a 
period of years; and (9) the absence of apparent local environmental 
factors influencing tree behavior, so that the results of the individual- 
tree studies would be truly comparative. 
