THE SWEET POTATO. 71 



The second group is formed by those varieties 

 which have only '* round" leaves. By a *' round" 

 leaf is meant a heart-shaped entire leaf. 



In the third group have been placed the *4ong- 

 leaved" varieties. In all well-formed, full-grown 

 leaves of these varieties the length of the large cen- 

 tral lobe, as measured along the median line from 

 the base of the lobe to its tip, exceeds the greatest 

 breadth of the same lobe. 



The "broad-leaved" varieties constitute the fourth 

 group. In these the greatest breadth, i. e., the base 

 of the central lobe, exceeds its length from the base 

 to the tip. 



Some varieties invariably have several types of 

 leaves, so that it is hard to tell which shape is the 

 most common. All varieties which normally have 

 well-developed, full-grown, ''round" leaves, as well 

 as ''long" or "broad," have been classed as "mixed- 

 leaved" in group five. 



In the key there has also been provision made for 

 varieties in which both "long" leaves and "broad" 

 leaves are frequent. 



It should be kept in mind that all references to 

 leaves, unless otherwise stated, apply only to full- 

 sized leaves developed at least two months after 

 planting, for the first leaves developing from a tuber 

 are usually "round" leaves, even in varieties which 

 later never produce them. The writer has even 

 observed them occasionally on plants with normal 

 "cut" leaves. 



Almost as characteristic as the shape of the leaf 

 is the size of the leaf. Weather and soil conditions 

 exert a certain influence on the size of plant parts ; 

 still, the author has convinced himself that neither 

 the difference between the compost soil used in 



