DOMESTICATED PLANTS BLAYDES 319 



the Baptist. The term "carat" has been applied to the carob bean 

 or seed, and these seeds were used originally as a unit of weight, the 

 carat. When mature, the seeds seem to be fairly uniform in size and 

 very hard, and the seed coat is impervious to water until it is scarified. 

 This imperviousness is a heritable characteristic and is found in the 

 seed coats of many species. It is of concern to horticulturists, agrono- 

 mists, foresters, and botanists. The waterproof coats of seeds and 

 some fruits are obviously correlated with longevity of the embryo. 

 The most prominent example is that of East Indian lotus {Nelmiibo 

 nucifera Gaertn.) (pi. 2, fig. 7). These are, botanically, fruits with a 

 single seed inside. The fruit coat (pericarp) is the structure that is 

 impermeable to water. When the fruit coat is notched germination 

 may occur within 10 days. A quantity of these fruits was recently 

 discovered in the depths of a peat bog in southern Manchuria. The 

 seeds were viable and would germinate readily upon scarification of 

 the pericarps. By the radiocarbon technique these seeds were shown 

 by Libby in 1951 to be about 1,000 years old. The seeds and rhizomes 

 have been used as food by peoples of Asia for many centuries. The 

 North American species, the water chinquapin {Nelivmho lutea 

 (Willd.) Pers.) was used as a source of food by the Indians. 



In any seed collection one of the most conspicuous to be found is 

 the castor bean {Ricinus communis) (pi. 2, fig. 6). This is not a 

 legume but belongs to the spurge family. Though widely naturalized 

 through the Tropics, it probably originated in Africa, with India as a 

 second-best choice. In the seed coats we find remarkable variations 

 in color and pattern, as well as in size and shape of the seeds. In 

 addition, the endosperm synthesizes castor oil, which youngsters 

 would readily proclaim as being a vile substance that should never 

 have happened. In addition to its medicinal value, it is of importance 

 industrially. 



Another member of the spurge family is the Para rubber tree 

 {Hevea hrasiliensis), with a few of its unusual seeds (pi. 2, fig. 8) ex- 

 hibiting characteristic patterns. It is a native of the Amazon. Al- 

 though found in negligible amounts in the seeds, a latex with high 

 rubber content is synthesized in the vegetative parts of the plant. This 

 tree is the chief source of natural commercial rubber. Although the 

 natives are said to have learned to make rubber balls from the latex, 

 and a crude syringe, and used it for waterproofing some clothing, 

 nothing was done about domestication until recent decades. I need 

 not dwell upon the importance of rubber in modern economy, but only 

 to mention our experiences after the Pearl Harbor disaster. 



Highly pigmented seeds are found distributed rather widely among 

 plant families: The sword bean {Canavalia gladiata) (pi. 3, fig. 11) 

 is from the Tropics of the Old World ; the large seeds are edible and 



