METHODS AND CONDITIONS OF EXPERIMENTATION IN THE STUDY 
OF CROWN-GALL AND HAIRY-ROOT. 
In order to prevent useless repetition, a brief description will be 
given of the methods and conditions under which each set of experi- 
ments was performed, the results of which are given in previous 
chapters and in the tables in the following portion of the appendix. 
EXPERIMENTS IN THE GREENHOUSE. 
All greenhouse experiments were conducted at the Mississippi 
Valley laboratory, St. Louis, Mo. Seedlings of various kinds of 
shrubs and trees were grown in pots and benches, as follows: All soil 
and pots were sterilized for three hours in an autoclave at a tempera- 
ture of 239° F. The benches were constructed of new pine and cypress 
lumber. Before filling the benches with soil they were washed with 
a strong solution of Bordeaux mixture. All seeds before planting 
were sterilized in one of two ways—either in concentrate sulphuric 
acid for ten minutes or for an equal time in a one-fifth of 1 per cent 
solution of mercuric chlorid, followed in either case by repeated 
washings in sterile water. In these experiments 6,176 plants were 
erown and ‘used in five years. 
EXPERIMENTS IN THE NURSERY. 
The experiments in nurseries were extensive and included the plant- 
ing of 143,763 apple seedlings and root grafts of 256 varieties during 
a period of six years. They were of two kinds, independent and 
cooperative. In each experiment all seedlings, cuttings, or scions 
were selected from the same stock, all root grafts’ were made and 
planted equally well in each portion, and all portions of each plat 
were of uniform soil and drainage and were cultivated equally well, 
all of the work being done by skilled workmen under the direction and 
personal supervision of the writer. Many experiments were dupli- 
cated in different localities, insuring greater accuracy in results. 
Independent nursery experiments.—These were conducted in nursery 
plats on land owned or leased by the Department and cultivated by 
its employees. There were three plats of the following description: 
Independent plat 1 was located near Louisiana, Mo., on a slightly 
sloping piece of upland consisting of a heavy, colluvial clay loam. It 
was situated so that it did not receive the overflow from adjacent 
a In all experiments where the term ‘‘root graft” is used, unless otherwise specified, 
reference is made to the form of root graft known as whip or tongue gralt. 
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