70 BULLETIN 815, U. S. DEPARTMENT OF AGRICULTURE. 
The object of these investigations has been to determine the 
behavior of trees of the different strains and of the individual-tree 
variations within the strain, to prevent the propagation of inferior 
strains, to develop practical methods for eliminating undesirable 
trees in established orchards, and to isolate and propagate the desir- 
able strains and superior trees within these strains through bud 
selection based on individual-tree performance records and _ inti- 
mate tree knowledge. 
The plan of work as followed in these investigations has been to 
secure individual-tree performance records in carefully selected 
plats of the Lisbon variety. Each tree is picked separately, the 
fruits assorted, counted, weighed, detailed notes taken, and other 
data obtained, so that after a series of years definite conclusions con- 
cerning strains and individual-tree behavior can be drawn. 
In these investigations five strains of the Lisbon lemon have been 
studied, their characteristics described, and the performance records 
of individual trees recorded. 
Some of the lessons taught by these studies include the discovery 
of the importance of bud variations, the comparative value of the 
different strains arismg from them, the need of eliminating the un- 
profitable strains and isolating the valuable ones through bud selec- 
tion, and the origination and introduction of improved methods of 
propagation for conserving and improving the production of the Lisbon 
lemon variety. The desirable strains can be isolated by means of 
careful bud selection based on individual-tree performance records 
and intimate tree knowledge. 
Undesirable healthy trees or inherently unproductive ones in 
established orchards usually can be successfully top-worked by using 
select fruit-bearing bud wood from performance-record trees. 
Undesirable unhealthy trees in old-established orchards can be 
replaced with desirable younger trees which have been propagated 
from selected fruit wood, provided proper attention is given to the 
preparation of the planting hole and, later, to care in wrigation and 
fertilization. 
Only fruit-bearing bud wood from superior parent trees which 
have been selected on the basis of their performance records and 
from intimate tree knowledge should be used for propagation or 
for top-working. 
The California Fruit Growers’ Exchange, a cooperative organiza- 
tion of 8,000 citrus growers, has established a bud-supply department 
as a result of these investigations. This department furnishes at 
cost to growers and nurserymen bud wood from superior performance- 
record trees. 
