2^2 PRODUCTION OF RACE:S AND SPECIES IN LEPTINOTARSA. 



The occurrence in nature of these variations from decemlineata is, as a 

 rule, rare. Owing to the abundance and concentration of decemlineata upon 

 potato fields, it is possible to examine huge series of these beetles. Some 

 idea of the infrequency of sports under normal conditions of existence can be 

 conveyed by the following observations made at various localities and for 

 different broods and years : 



West Bridgezvater, Massachusetts, 1895. — First brood: Examined from one field 

 13,210 beetles, no sports; from a second field, 11,841, i sport, form melanicum. Second 

 brood: From same field as first brood, 21,400 beetles, i sport of form melanicum. 



Cold Spring Harbor, Long Island, iSgg. — First brood: Examined from one field 

 14,600 beetles, 2 sports — forms pallida, melanicum. Second brood: From same field, 

 13,500 beetles, no sports. 



Cabin John Bridge, Maryland, igoo. — Second brood: From one field 11,792 beetles, 

 82 sports — forms melanicum, minuta, pallida, tortuosa. 



McKeesport, Pennsylvania, 1900. — Second brood: 9,460 beetles, no sports. 



Yellow Springs, Ohio, 1901. — First brood: 16,002 beetles, no sports. Second brood: 

 14,200 beetles, 17 sports — pallida, minuta, immaculothorax. 



Chicago, Illinois, 1902. — Hibernating beetles from collections on lake beach, 10,109 

 beetles, no sports. First generation: 12,019 beetles, 2 sports — form pallida. Second 

 generation : 17,008 beetles, no sports. 1903, from same localities, 16,200 beetles of the 

 hibernating generation, i sport — form minuta. First generation: 13,100 beetles, no 

 sports. Second generation: 12,400 beetles, no sports. 



San Antonio, Texas, 1904. — Second brood: 1,100 beetles, 12 sports — tortuosa, albida, 

 minuta. 



From these records in nature we see the great rarity of these forms, and 

 taking all the counts, out of 207,891 beetles examined there were 118 sports, 

 or in the ratio of 1,761 to i. This high ratio, however, is due to the lot from 

 Cabin John Bridge, where there were an enormous number of sports, due to 

 most unusual conditions of environment. If we remove these the remaining 

 196,099 show 36 sports, or in the ratio of 5,447 to i. Taking all the available 

 data gathered from 1894 to 1904, I find that on the average about i beetle 

 in 6,000 is of the class which is designated as sports, discontinuous varia- 

 tions, or mutants. 



These figures demonstrate two interesting points : First, the average rarity 

 of these variations, and the necessity of handling large numbers of specimens 

 to discover them^; second, the great production of these under extreme and 

 sudden changes of environment as at Cabin John Bridge. I have already 

 described the same phenomenon in the section on variation, wherein I showed 

 that place variation, when extreme, was accompanied by a great increase in 

 the number of these variations produced, as compared with the normal ratio 

 of production. 



The finding of these extreme and permanent variations in nature at the 

 right tim.e for experimentation, and the successful breeding of them is neces- 

 sarily a matter of chance and open to great liability to failure. In my 

 experience these sports are in nature mostly found singly, and in culture must 



