BUREAU OF PLANT INDUSTRY. 269 



station, where individual tree propagations are under way, it is 

 noted in the case of the apple that the stand percentage from dif- 

 ferent individuals varies considerably. The . direct propagation of 

 apple varieties from scion roots has so far given stand percentages 

 too low to make the method of particular use. 



At Altadena and San Dimas, Calif., the work this year has 

 shown that the sour orange, the stock commonly used in California 

 for orange, lemon, and grapefruit, can be propagated by root cut- 

 tings. This ofi'ers a practical way of propagating a strain of sour 

 orange known as the Spanish strain, which seems to be the most 

 desirable strain studied. The increase of desirable types of citrus 

 stocks from root cuttings has been very successful at the Altadena 

 nursery. While the cuttings under some conditions require some 

 time to start, their subsequent growth is rapid and very good stands 

 have been secured. In all the work in vegetative propagation 

 efforts are being made to devise methods capable of commercial 

 application and to determine the most desirable age and size of 

 material to use. 



CITRUS FRUITS. 



Breeding. — The breeding of new varieties and stocks, chiefly 

 through hybridization, to secure extra hardiness, disease resistance, 

 and adaptation to special soil and climatic conditions, together with 

 other desirable qualities, has resulted in bringing into use several 

 new hybrids. Six of these have been named and described during 

 the past year, three resulting from crosses of the citrange and 

 kumquat, called citrangequats (trigeneric hybrids), and three from 

 crosses of the lime and kumquat, called limequats. Improved 

 methods for the rapid propagation of these and other citrus plants 

 by the use of fine twig cuttings have been worked out and a pre- 

 liminary description published. 



To safeguard the introduction of citrus plants and relatives needed 

 in breeding work and for field trial in the United States improved 

 technique in quarantine procedure and propagation has been de- 

 veloped which may well be termed " aseptic propagation." Many 

 of the new features of this system, both mechanical and horticul- 

 tural, may with advantage be applied to commercial greenhouse 

 practice. A circular has been prepared for publication describing 

 the various devices invented and the methods used as a protection 

 against insect infestation and infection by microorganisms. 



The work of bud selection for the improvement of citrus varieties 

 has been carried on in Florida and Alabama. In Alabama the work 

 has progressed so far that nearly all the buds for growing Satsuma 

 nursery trees are now taken from performance-record trees. In 

 Florida a progeny grove from selected parent trees is being devel- 

 oped at the branch experiment station in cooperation with the 

 Florida Agricultural Experiment Station, which in future years 

 will serve as a source of bud supply for growers and nurserymen. 



Commercial 'performance records. — The California Fruit Growers' 

 Exchange, a cooperative organization of citrus growers, established 

 in May, 1917, a bud department for the purpose of making avail- 

 ftble to nurserymen and growers the results of the bureau's investi- 

 gations upon bud selection in correlation with tree-performance 



