94 VARIATION IN LEPTINOTARSA. 



In a former paper ( 1902) I have used the term "secular variation" to desig- 

 nate this phenomenon, and have advanced certain views regarding the study 

 of variation. It was shown that biometric work must take into account this 

 fluctuation in the population, and the term "place mode" was expanded to a 

 broader significance. Pearson (1902), however, objected to my use of the 

 term "place mode" in that "it might refer to any constant whatsoever of the 

 frequency to the mean, mode, variability, or indeed to the whole frequency 

 distribution itself"- and I believe that the point is well taken. Shull (1904) 

 proposes the term "place condition" or "place habit" to designate the phenom- 

 enon for which I used the term "place mode." This is, I believe, a good term, 

 not open to biometric or other objections, and I shall use it in this paper. In 

 the interest of uniformity and for certain philological reasons, I use the term 

 "place variations" to designate what I called "secular variations" in 1902. 

 We recognize, then, (1) place variation, or the variation in any given species 

 in the same locality from generation to generation, or from season to season, 

 or year to year; (2) place condition, as the state prevailing in the population 

 of a given species at a particular locality during one generation; and (3) 

 place constant, determined for the population of a given species at a given 

 locality for one generation. 



, The existence of the phenomenon of place variation was discovered early 

 in the study of this material and was at first interpreted as indicating rapid 

 change in condition. But in succeeding generations, when the variations 

 moved back to the old original condition, the phenomenon with which we now 

 have to deal was recognized. In the genus Leptinotarsa not all species show 

 this phenomenon alike, but all do to some extent. 



In L. decemlineata the place variation is extreme, and differs in degree in 

 different places. We can best illustrate this by data from specific localities. 

 Hence I shall give the place variations of decemlineata for a locality in West 

 Bridgewater, Plymouth County, Massachusetts, and for Chicago, Cook 

 County, Illinois, for several generations at each place. 



At the first locality collections of L. decemlineata were made during the 

 years 1895 to I 9 2 or during a period of 16 generations. They were collected 

 from potato fields in which there were about 12 inches of soil, 18 inches 

 to 2 feet of clay subsoil, and a stiff blue till clay beneath. Various characters 

 of the beetles collected at this locality were studied. The table of the distri- 

 bution of frequencies (table 33 a) indicates the proportion of light to dark 

 color on the epicranium and the variations that have been found from genera- 

 tion to generation. Table 33 b shows the corresponding variation in the pro- 

 notum ; table 33 c that in the elytra ; table 33 d that in the abdominal seg- 

 ments, and table 33 t the variation of males and females in size. In table 33 F 

 are given the polygons of place condition for the species taken as a whole. 

 It is evident that in these 16 generations there is abundant place variation. 



