138 America's Crop Heritage

ing of plant materials for both crop and industrial uses, as well
as the cataloging of present genetic stocks, and the preservation
of basic germ-plasm for future breeding programs.
 Regional activities have been centralized around four primary
introduction stations at Pullman, Washington for the Western
Region; Ames, Iowa, for the North-Central Region; Glenn
Dale, Maryland, for the Northeastern Region; and Experiment,
Georgia, for the Southern Region.
 Foreign seeds received by the Division of Plant Exploration
and Introduction are sent to these primary introduction stations
for repropagation and distribution to state experiment stations.
The growing plants are given a preliminary check for growth
and disease factors at the primary stations, but detailed evalua-

 TABLE 8
 FRUIT CROP VARIETIES INTRODUCED BY OFFICE OF SEED
 AND PLANT INTRODUCTION

 No. of Varieties
 Crop Introduced
 Apples. ................................... 600
 Avocadoes................................ 353
 Blackberries............................... 100
 Jujubes ................................... 225
 Mangoes. ................................. 498
 Nectarines. ................................ 50
 Peaches................................... 500
 Pears...................................... 700
 Oriental persimmons. ....................... 600
 Plum s .................................... 450

 Based upon an estimate made in 1928 by B. T. Galloway, Department pathologist.

 tion of the plants and work on breeding programs is left to
 the experiment stations.
 To insure the passing on of the "pure" strains as they are
 received, the primary introduction stations frequently resort to
 hand pollination of certain species that would otherwise cross
 freely by insects or windborne pollen. (See Fig. 3). In hand
 pollination it is necessary to keep both the male and female
 flowers covered to insure the desired parentage.
 Where it is impractical either to isolate or hand pollinate
 large numbers of normally insect or wind-pollinated species, the
 plants are increased by vegetative cuttings. For growing areas