128 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
WORK OF THE UNITED STATES DEPARTMENT OF 
AGRICULTURE ON PLANT HYBRIDISATION.* 
By Hersert J. WEBBER, in charge of the Plant- breeding Laboratory. 
WHILE some work on plant-breeding has been in progress in the United 
States Department of Agriculture for a number of years, until recently it 
has been almost wholly in the line of simple selection without the direct 
application of hybridisation and cross-breeding. The work on hybridisa- 
tion proper as a means of securing variations and improvements was 
started only a few years ago, and as yet all the work is in an uncompleted 
state. Some points of interest have been secured, however, and I shall 
briefly describe some of these in this paper. The work thus far under- 
taken has been mainly on Oranges, Grapes, Pineapples, Pears, Apples, 
Wheat, Corn, and Cotton. It will not be possible to discuss all of the 
experiments in progress, and features will be selected here and there 
which it is thought will be of interest to the members of the Conference. 
The work on Oranges and Pineapples which will be described has been 
conducted by the writer in conjunction with Mr. Walter T. Swingle, and 
equal credit should be given him for any factors of importance brought 
out. Owing to the unfinished condition of the work this paper will largely 
treat of the improvements which it is desired to secure, with an indication 
of the progress made. 
ORANGE HYBRIDISATION. 
The work on the hybridisation of the Orange and other citrous fruits 
was begun in 1893, but was greatly interrupted by the severe freezes in 
the winter of 1894 and 1895, and again last winter, February 1899, 
when a number of the hybrids which would have fruited this year were 
frozen down. We have secured about 2,000 citrous hybrids which are 
being grown and tested, but none of these have yet fruited, and the com- 
parisons given below are accordingly based entirely on foliage characters, 
habits, &e. 
A Hardy Orange.—The most important development that we are 
striving to produce in citrous fruits is a hardy Orange which will withstand 
the severe frosts that occasionally cause such serious damage in the Orange 
regions of the United States. This we hope to secure by hybridising the 
Japanese Trifoliate Orange (Citrus trifoliata) with the various varieties 
of the Common Sweet Orange (C. awrantiwm sinensis). The Trifoliate 
Orange is a deciduous trifoliolate tree which is perfectly hardy as far 
north as New York, and is coming to be used extensively as a hedge 
plant. The fruit is small and bitter, and is generally considered worthless : 
* In this paper the term “ hybrid” isused, comformable to the Centwry Dictionary, 
as a generic term to include all organisms arising from a cross of two forms noticeably 
different, whether the difference be great or slight. Adjectives are sometimes used to 
indicate the grade of the forms resulting froma cross, such as racial, varietal, or 
bigeneric hybrids. Where a hybrid of two races or species is crossed with a third 
race or species a triracial or trispecific hybrid would result. (See discussion on this 
point in Year-book, United States Department of Agriculture, 1897, p. 384.) 
