Analysis of Heterogeneity in Complex Chaeactbes 339 



These locations are shown in plate 19, and while close together and easy of 

 access by transportation, are diverse in their conditions of life, so that as far as 

 possible any influence of localized conditions or other environmental factors 

 could be detected and made the basis of experimental analyses. The three gen- 

 eral regions were the Valley of Mexico, Eio Atoyac Valley, and the western 

 slopes of Volcano of Arizaba. / 



The GhapuUepec colony — A location 1 kilometer southwest of the Palate of 

 Chapultepec (near Mexico City), in the open plain just above an old shore-liae, 

 of Lake Texcoco, was chosen in 1903, and regular observations were made begin- 

 ning with the first generation of 1904 and continued without interruption until 

 the middle of 1910. Thirteen generations were thus observed. This location is 

 an open savannah, sloping from the hills to the west of the valley towards Lake 

 Texcoco. It is well watered by rain and less influenced by drainage operations 

 than the location about the Sierra Guadalupe. Further, the observations of the 

 meteorological conditions obtained at Tacubaya were fairly applicable to the 

 location. 



The Texcoco colony. — Another location was chosen in 1903 on the east shore 

 of Lake Texcoco near the town of Texcoco, Federal District, Mexico. Two rea- 

 sons determined this location ; first, its being an old lake-bed and still at about 

 the lake level, so that it differed strikingly in soil-water supply from the Chapul- 

 tepec Station, and second, the fact that fairly systematic meteorological observa- 

 tions were made in the town. These latter, although not exactly what I would 

 like to have had, were still a fair measure of the difference between the two 

 localities, one to the west and the other to the east of Lake Texcoco. Observa- 

 tions were begun in 1903 and continuicd until the close of 1909 or 13 generations. 



The Tlalnepantla colony — In the north-central portion of the basin near 

 Tlalnepantla, Federal Disliict, Mexico, where meteorological observations were 

 also to be had, a location was chosen near the Eio Tlalnepantla, along the border 

 of some cultivated fields. Observations were begun here in 1903 and continued 

 until 1907, 10 generations being under observation. In addition to these loca- 

 tions records were also continued near the foot of the Sierra Guadalupe until 

 the end of 1907, or for 8 generations. Other records were also made for loca- 

 tions near San Angel, Santa Fe, Tlalpam, and Huehuetoca, also in the valley of 

 Mexico; at all, results the same in principle but not in detail were obtained, and 

 these, together vnth the fact that meteorological observations fairly applicable 

 to Chapultepec, Texcoco, and Tlalnepantla were available, led to the concentra- 

 tion of effort upon the colonies at these points in the valley of Mexico. 



RIO ATOYAC VALLEY. 



Only one location near the city of Puebla, State of Puebla, Mexico, was estab- 

 lished. A number of locations were examined, but the absence of climatic rec- 

 ords of any value and the difficulty of having them made decided the location of 

 the Puebla colony. On the open plain about 4 kilometers north of the city, 

 in uncultivated land used for pasture, a thriving colony was found, and to the 

 climatic conditions of this location the meteorological records of two stations in 

 the city of Puebla were fairly applicable. Observations were begun in 1903 and 

 continued until 1908, or 13 generations in all. 



