Active Causes of Organic Evolution 183 



sunny situation, are of a purple-crimson tint, while a variety 

 of it, that is not unfrequent in some of the Gulf States, is uni- 

 formly of an intense deep crimson-purple color. But even 

 S. purpurea when it grows — as it occasionally does — in the 

 rather deep shade of swamp thickets is always uniformly green, 

 or shows only purple lines along the back of the throat. Like 

 changes can be produced mth almost measurable exactitude 

 under cultivation. 



We conclude therefore that red pigmentation is being slowly 

 developed by Sarracenias; that the capacity for formation 

 of it resides in the cell contents; that in S. minor it is not per- 

 ceptible as a rule, and in any case is feeble; that owing to en- 

 vironal and mainly Hght action it is being more and more 

 richly formed, and as aiding in insect attraction is being se- 

 lected; that such color may have existed in greatly more primi- 

 tive ancestors of the group, belonging to the Incompletse, 

 if we may judge from analogy with other groups, but the envir- 

 onal stimulus may have waned, and the color may have receded 

 to the disappearing point, to be again called forth as above, 

 when life relations were favorable. 



As John Bartram Well observed nearly 150 years ago, the 

 Venus fly-trap (Dioncea muscipula) shows equally sharp color 

 changes, according to natural or artificial environal states. 

 For it may vary from pale yellow-green, in deep shade, to a 

 deep uniform purple, in hot savannah situations. 



Another case might be cited that greatly impressed the 

 writer. iVfter kno%nng and experimenting with the Sensitive 

 Plant for fully a decade in greenhouses, where it always was 

 of bright delicate green color, with occasional faint traces 

 of brown color in the stem, specimens were planted out in his 

 garden twenty years ago during early August. These were 

 exposed to atmospheric conditions for about seven weeks that 

 were decidedly different from those of a slightly shaded hot- 

 house. They often were exposed to hot bright light during 

 day, and rather cold night states from the latter i>art of August. 

 All of the plants developed a dark reddish i)igment in their 

 stems and leaf stalks, while the plants generally in continuing 



