9 oo 



ECOLOGY 



There are some instances where color variation may not be due to external 

 factors. Hepatica plants, in apparently similar conditions, exhibit various colors 

 from pink to blue. Perhaps the most probable instance of " inherent " color char- 

 acters is in the albinos, which seem to have white {i.e. unpigmented) flowers in any 

 habitat; such albinos are known in many plants (as in Lupinusand Sisynnchium), 

 and in some cases there are comparable variegated flowers (as in Viola cucullata) . 

 Albinos commonly are regarded as sports or mutants, but the possibility of external 

 determining factors even here is suggested by the reported pigmentation of Trillium 

 albinos that have been transplanted to a new habitat. 



Variations in the size and number of floral organs. When plants 

 are grown in very poor nutritive conditions, the number of flowers on 

 each individual is much reduced, and sometimes (as in the poppy) the 

 size of the flower also is reduced. Weakened illumination may cause 

 a decrease in flower size, particularly in the size of the corolla (as in 

 Mimulus) ; by contrast it is to be noted that in xerophytic alpine habi- 

 tats, in spite of the marked reduction of other organs, there is no marked 

 reduction in flower size, probably because of the intense illumination 

 (figs. 1051, 1052). In poorly nourished specimens of Agrimonia, the 

 stamen number may be reduced from about twenty to five. When the 

 poppy is grown in dense cultures, the number may be reduced from 

 thirty or forty to six; this result is most significant, since in this group 

 the large number of stamens is an important taxonomic character. 

 Equally significant is the carpel variation in the poppy; in well-nourished 

 individuals there may be one hundred and fifty carpels, but in poorly 

 nourished individuals the number may be reduced to four. In Chrysan- 

 themum and in some other composites, the number of ray flowers varies 

 with the nutrition, well-nourished plants having the largest number of 

 such flowers. A remarkable situation is presented in Sempervivum, 

 in which there have been produced all gradations between flowers and 

 vegetative shoots; some flowers lack corollas, others lack stamens and 

 pistils, and even the calyx, which usually is the most certain of develop- 

 ment of floral organs, sometimes is absent, in which event the bracts 

 alone represent the floral organs. In this genus also it is possible 

 to induce the transformation of stamen primordia into carpels, or 

 of carpel primordia into stamens. Similar results have been obtained 

 in Veronica (p. 892). 



Variations in flower form. Perhaps the most significant of all the 

 variations in reproductive structures are those involving changes in form, 

 since they have to do with the very fundamentals of classification, and 

 therefore are likely to shed important light upon the processes of evolu- 



