GO ORIGIN OF CULTIVATED PLANTS. 



decidedly of modern introduction. It is propagated by 

 budding. 



Botanists are divided in opinion whether the innu- 

 merable varieties of manioc should be regarded as form- 

 ing one, two, or several different species. Pohl ^ admitted 

 several besides his Manihot utilissima, and Dr. Miiller,^ 

 in his monograph on the Euphorbiaceae, places the variety 

 aipi in an allied species, M. ixthnata, a plant cultivated 

 with the others in Brazil, and of which the root is not 

 poisonous. This last character is not so distinct as might 

 be believed from certain books and even from the asser- 

 tions of the natives. Dr. Sagot,^ who has compared a 

 dozen varieties of manioc cultivated at Cayenne, says 

 expressly, " There are maniocs more poisonous than 

 others, but I doubt whether any are entirely free from 

 noxious principles." 



It is possible to account for these singular differences 

 of properties in very similar plants by the example of 

 the potato. The Manihot and Solanum tuberosum 

 both belong to suspected families (Eu]yhorhiacece and 

 Solanacece). Several of their species are poisonous in 

 some of their organs; but the fecula, wherever it is 

 found, is never harmful, and the same holds good of 

 the cellular tissue, freed from all deposit ; that is to say, 

 reduced to cellulose. In the preparation of cassava, or 

 manioc flour, great care is taken to scrape the outer skin 

 of the root, then to pound or crush the fleshy part so as 

 to express the more or less poisonous juice, and finally 

 the paste is submitted to a baking which expels the 

 volatile parts.^ Tapioca is the pure fecula without the 

 mixture of the tissues which still exist in the cassava. 

 In the potato the outer pellicle contracts noxious quali- 

 ties when it is allowed to become green by exposure to 

 the light, and it is well known that unripe or diseased 

 tubers, containing too small a propertion of fecula with 



^ Pohl, Planiaruin Brasilice Icones et Descriptiones, in fol., vol. i. 



^ J. Miiller, in Prodromus, xv., sect. 2, pp. 1062-1064. 



3 Sagot, Bull, de la Soc. Bot. de France, Dec. 8, 1871. 



* I give the essentials of the preparation ; the details vary accoi'ding 

 to the conntry. See on this head : Aublet, Gmjane, ii. p. 67 ; De- 

 conrtilz, Flora des Antilles, iii. p. 113; Sagot, etc. 



