The impact of a second World War has served to bring home more forcibly than ever the dependence of our modern civilization on plants and plant products. Once the normal sources of supply were cut off and the exigencies of the war brought about, an increased demand, many fibers, oils, fats, insecticides, and drugs, as well as rubber, were quickly classified as strategic materials. An adequate food supply, both for domestic use and for export to less fortunate countries, became of paramount importance.
Greater production both of food and of the strategic materials was imperative. In the case of domestic plants this involved merely an increase in acreage and the utilization of improved methods of cultivation and harvesting. Where foreign plants were concerned, attention was usually first directed to the possible introduction and establishment of these species in the Western Hemisphere. In cases where this was impracticable, it was necessary to secure satisfactory substitutes. Many formerly little-known species suddenly became of great importance.
The past few years have also seen many advances in the field of medicine and the utilization of drugs obtained from plants that were virtually unknown a decade or so ago. The result of all this effort has been a definite change in the agricultural and forest practices of the various countries, particularly those of this hemisphere. Sorne of these changes will be permanent, others more transitory in nature.
In the present revision an attempt has been made to take cognizance of these matters and to evaluate them as to their possible future significance. In consequence the subject matter has been completely revised and several chapters have been entirely rewritten. Some 140 additional species are discussed and new illustrations have been added.
In the present unsettled state of world affairs statistics of production in the several countries and of imports into the United States vary so from year to year that they are of little value. Consequently, it has seemed advisable to reduce such statistics to a minimum.
The list of species includes all new species discussed in the text, and the nomenclature has been carefully checked and brought up to date. In order not to be too unwieldy the bibliography is restricted to works that have been published since 1936.
The author wishes to express his appreciation to those of his friends and colleagues who have made suggestions and critical comments or