182 Causes and Course of Organic Evolution 



ening, glucoside secretion, these may readily be suppressed, 

 or called forth for a long period in wavering manner. And 

 only after long generations of growth, amid like surroundings, 

 does the ''character" become "fixed" for the time being, or 

 permanently if like environment be continued. 



As a case in point we might cite coloration of the pitchers 

 in the seven species of Sarracenia that are all native to North 

 America, and which the writer has studied, in their native 

 haunts, over thousands of miles of territory. The most primi- 

 tive species unquestionably is S. minor, whose pitchered leaves 

 are most usually of a pale green, more rarely of a brownish 

 green, hue. S. flava and S. Sledgei rank next in advancing 

 specialization, are both bright green, with veinings of crimson 

 behind or along the throat of the pitchers, or in a frequent 

 variety of S. flava the entire back of the throat is of a rich 

 crimson hue. But, in sunny meadows that are wet in winter, 

 and whose soil becomes hard and dry in summer, all vari- 

 eties of both species may be gathered near at hand or in distinct 

 localities, in which the color spreads from the throat, first 

 along the vascular bundles of the pitcher, and in others even 

 throughout the tube generally, so that this becomes of a deep 

 crimson-purple color, and attracts the eye at many yards 

 distance. The writer has often removed numerous groups 

 of these to greenhouses where they have been watched, and 

 where natural conditions could be imitated or altered. 



He has clearly proved that the amount of pigmentation 

 is determined by light intensity, combined with relative dry- 

 ness or moistness of soil, the smallest, firmest, and most richly 

 pigmented being those that were simultaneously exposed to 

 the brightest light and to moist soil conditions at one period, 

 becoming dryest soil conditions at another. Even by suf- 

 ficient shade, it is possible to grow leaves of a uniformly green 

 color, that in the previous season were crimson-purple. 



But S. rubra, S. Drummondii, S. psittacina, and S. purpurea 

 show steadily advancing specialization, alike in pitcher and 

 in floral details. They show like advance also in pitcher color, 

 so that plants of *S. purpurea, growing as they usually do in 



