i66 



certain varieties, and of the lack of distinguishing marks of cer- 

 tain varieties, especially those with white seed, much difficulty has 

 been experienced. The varietal types of Lima beans being not well 

 fixed, it seemed advisable to limit our key of this species to the 

 separation of the varieties into well-defined groups. 



While the writer is satisfied with the efficiency of the key under 

 ordinary conditions, he is conscious of its many imperfections, and 

 finds it necessary to indicate the following limitations and pre- 

 cautions : 



1. Inasmuch as seed varies somewhat in size and coloring accord- 

 ing to the locality, this key is more applicable to northern grown 

 seed. As a very large proportion of our bean seed is produced in 

 the North, this is not a serious limitation. 



2. Fresh seed only (seed of the last seasons crop) should be 

 used, as the markings on old seed are not distinct. 



3. Only thoroughly ripened and cured seed should be used. 

 Normally black seed, if harvested prematurely, will be greenish 

 brown in color. In samples where black and greenish brown speci- 

 mens are found it is necessary to select the natural black type. 



4. Only healthy seed should be used, for diseased seed is usually 

 undersized or otherwise deformed. 



5. In any sample it is necessary to select typical specimens. 



6. Accuracy in measurement is necessary ; this is especially true 

 when the term " twice as long as broad " is used. An error of a 

 fraction of a millimeter in width will often throw the seed in the 

 wrong group. It is sometimes necessary to measure a number of 

 typical specimens and take the average. Fine pointed dividers and 

 a metric rule will answer the purpose, but the use of calipers equip- 

 ped with a metric scale which will indicate the measurement after 

 simply drawing the points over the seed in the direction desired, is 

 recommended. 



The dual or dichotomous system of tabulating has been adhered to, 

 so that if the first descriptive sentence does not agree with the 

 sample in question, the second or alternative must agree, assuming, 

 of course, that such a variety is treated in the table. New forms 

 are sure to appear from time to time to which this key cannot be 

 applied. If in doubt as to agreement it is well to try the alterna- 

 tive before proceeding; and since there are so many shades of 

 brown, this precaution is specially applicable to brownish colored 

 seed. 



