58 



^^\RIOUS FOOD-PLANTS 



Flu. 50. — Sweet Potato {Ipufiiatl BidaOfs, AIoriHiig-(.il'"ir\- l''aijul,\-, Trw/- 

 vubulacca). Stem, leaves and roota. X i. (Redrawn.) — Plant a jn r- 

 cnnial (i. e. growing more than two years) with creeping stems l:ie- 

 coming 2-3 m. long; leaves dark green, glossj'; flowers purple, closely 

 resembling those of the common morning-glory; roots l)ecoming fleshy', 

 sw'eet, and yellow within; fruit dry. 



herbage-vegetables are found to l)c a good deal like earth- 

 vegetables. The chief difference is that the former have, on 

 the whole, a somewhat larger percentage of water, and a 

 smaller amount of digestible carbohj^drate. As against these 

 deficiencies, however, there is a, decidedly larger proportion 

 of proteid in relation to the other nutritious materials. For 

 example in lettuce which has at once the most water and the 

 least proteid of any of the herbage-vegetaljles given in the 

 table, we find that about one-third of the nutritive material 

 (representing nearly one-Ciuarter of the total weight exclusi\-e 

 of water) i.s proteid; while in the .sweet pottito (which of all 

 the earth-vegetables given, has the least water and next to 

 the most proteid) the proportion of proteid to other nutrients 

 is approximately 1 to 12 (lieiug to tlie t(.)tal weight of the 

 material dried, nearly as 1 to 18). 



