494 POPULAR SCIENCE MONTHLY. 



the ancient agricultural peoples of the Tropics.* At present we have 

 only incomplete and scattered data collected incidentally by mission- 

 aries, travelers and professional botanists who did not appreciate their 

 opportunities from the agricultural point of view. But even these mis- 

 cellaneous facts are often of unexpected interest. Thus, we know that 

 in Central America the use of leguminous shade-trees in cacao planta- 

 tions was adopted by the Spanish colonists from the natives who fur- 

 nished even the name ' mother of cacao, ' by which the species of Ery- 

 thrina and other leguminous trees are still known in Spanish America. 

 The Indians, of course, were not aware that the roots of the Leguminosas 

 develop tubercles for the accommodation of bacteria able to fix atmos- 

 pheric nitrogen; they believed that the ' madre de cacao ' supplied 

 water for the roots of the cacao, a fanciful idea still credited by many 

 planters of cacao and coffee. In the Pacific we encounter a similar 

 fact with reference to the yam bean (Pachyrhizus) , a leguminous vine 

 with a fleshy edible root. The natives of the Tonga Islands no longer 

 cultivate Pachyrhizus for food, but they nevertheless encourage its 

 growth in their fallow clearings in the belief that it renders them the 

 sooner capable of yielding large crops of yams. Such anticipations of 

 the results of modern agricultural science are of extreme interest, but 

 it is still uncertain whether similar knowledge exists in other archipela- 

 gos of the Pacific, or on the American continent where Pachyrhizus 

 probably originated. The botanists report it as ' a common weed in 

 cultivated grounds,' and we learn further that in the absence of better 

 material, the people of Fiji use the fiber for fish-lines, and that the 

 plant sometimes figures in an unexplained manner in their religious 

 ceremonies. 



Our knowledge is far from complete regarding even the present 

 distribution of the principal tropical food plants, but the need of fur- 

 ther investigation should not obscure the striking fact that several of 

 the food plants with which the Spaniards became acquainted in the 

 West Indies were also staple crops on the islands and shores of the 

 Pacific and Indian Oceans, and even across tropical Africa. 



Ethnologists who might have appreciated the bearing of this have 

 passed it by because of the absence of maize or Indian corn among the 

 Polynesians. But in addition to the unreason of accepting negative 

 evidence as an offset for positive fact, two pertinent considerations 

 have been overlooked, first, that most of the varieties of maize do not 

 thrive in the humid climates of the equatorial islands, and, second, that 

 maize was found by Captain Moresby in cultivation with yams, sweet 



* Even the cosmopolitan tropical weeds are worthy of careful study from 

 this standpoint. After excluding aquatic, swamp-land and strand species, See- 

 man found 64 genuine weeds in Fiji, of which 48 were common to America, 

 while only 16 were held to be Old World species. 



