58 



VARIOUS FOOD-PLANTS 



Fig. 56. — Sweot Potato (Ipomaca Batatas, Morniug-Glory Family, Con^ 

 volviilaceoe) . Stem, leaves and roots. X i. (Redrawn.) — Plant a per- 

 ennial (i. e. growing more than two years) with creeping stems be- 

 coming 2-3 m. long; leaves dark green, glossy; flowers purple, closelj' 

 resembling those of the common morning-glory; roots becoming fleshy, 

 sweet, and yellow within; fruit dry. 



herbage-vegetables are found to be 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 carbohydrate. 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-vegetables given in the 

 table, we find that a])out one-third of the nutritive material 

 (representing nearly one-quarter of the total weight exclusive 

 of water) is proteid; while in the sweet potato (which of all 

 the earth-vegetables given, ha.s the least water and next to 

 the most proteid) the proportion of proteid to other nutrients 

 is approximately 1 to 12 (being to the total weight of the 

 material dried, nearly as 1 to 18). 



