\ 



68 THE SWEET POTATO. 



The distingTiisliing characters must be reasonably 

 permanent, i. e., the great majority of the descend- 

 ants of the same plant grown together nnder normal 

 conditions ought to maintain uniformity in those 

 characters. 



The distinguishing characters ought to be so clear 

 that they can easily be determined. 



It is very desirable in a key that it should take 

 up the characters in such an order that varieties 

 which differ but little from each other and are very 

 likely closely related can be easily compared. This 

 is perhaps best effected by using the same characters 

 in classifying all varieties. 



As it is not always possible to determine all the 

 characteristics of a varietv at one time, the char- 

 acters given should be as abundant as possible, so 

 that the variety may be determined even if not all 

 parts of the plant are present. 



The key, as evolved below, was elaborated to meet 

 these different requirements. 



The distinguishing characters, as utilized in the 

 key, were determined in the following manner : 



Thirty-five so-called varieties were obtained from 

 the Agricultural Experiment Stations at Washing- 

 ton; Baton Rouge, La,; Experiment, Ga.; and from 

 Mr. Rose, of Wilmington, Del., and Mr. Trouncer, 

 of AVenonah, N. J. All these were planted in the 

 same patch at W^enonah and studied throughout the 

 season. 



All types of leaves produced by all varieties, as 

 the season advanced, were collected and pressed. 

 Photographs were taken of typical hills and vines 

 of each variety to show characteristic growth and 

 leaf arrangement. Careful notes were taken repeat- 

 edly and independently of the comparative length 



