318 ANNUAL REPORT SMITHSONIAN INSTITUTION, 195 4 



By means of this new kind of propagule a very successful land flora 

 became established, even over relatively arid regions, on all the con- 

 tinents except the Antarctic. All land habitats were more fully occu- 

 pied by plants than before. The total vegetation mass was greatly 

 increased, which in turn changed the characteristics of soils. The 

 stream of heritable variations that occurred in seed plants is almost 

 beyond comprehension. These occurred mainly before there were any 

 humans in existence. The beginnings of some understanding of such 

 matters is but a century old. Taxonomists now recognize about 10,000 

 genera and at least 300,000 species of seed plants. Many more will un- 

 doubtedly be discovered as time goes on. 



SOME HERITABLE VARIATIONS IN SEEDS 



Perhaps it is trite to point out that probably in every species of 

 seed plant certain heritable potentialities may become expressed only 

 in the seeds. Such were some of the characters in garden peas {Pisum 

 saiiviMn L.) which Mendel studied in his classical work of nearly a 

 century ago — smooth and wrinkled seed coats, and yellow and green. 

 From these seed characters (pi. 1, fig. 1) as well as variable characters 

 from other parts of the pea plant, the fundamental principles of he- 

 redity applicable to both plants and animals were discovered. Though 

 lost for nearly forty years, these principles, when rediscovered, 

 sparked the new science of genetics at the beginning of the twentieth 

 century. However, peas were not new to man in Mendel's time. They 

 are among his oldest domesticated plants, the oldest recognizable re- 

 mains dating 3000 B. C. from the Swiss lake dwellings of the Stone 

 Age. The place of origin is in doubt, but may have been in the Medi- 

 terranean region or in western Asia. The pea as we know it is a culti- 

 gen, and botanists have been unable to locate it in the wild state. 



The kidney bean {Phaseolus vulgaris) (pi. 1, figs. 3, 4) probably 

 originated in Brazil. However, its greatest diversity was reached in 

 Guatemala and Mexico. The Peruvians were cultivating it about 

 4,500 years ago. It was widespread among North American Indians. 

 More than 500 varieties have been given names in recent times. Much 

 the same story may be told for the lima bean {Phaseolus lunatus) (pi. 

 1, fig. 2). This illustration shows something of the remarkable diver- 

 sity of lima beans as to size, shape, and color pattern. These are from 

 a collection of present-day varieties found in Guatemala and Mexico. 

 These two species of beans are sources of basic food materials used by 

 millions of people. 



The carob, locust bean, or St. John's bread {Ceraforiia sUiqua), a 

 leguminous tree of the Mediterranean region (pi. 1, fig. 5), has pods 

 that are used for human consumption as well as feed for swine and 

 cattle. The pods have been identified by some with the locusts of John 



