VARIATION 25 



(<) Moisture and Plumage Color. Beebe experimented with the pigeon, 

 Scardafella inca. This species, as found in North and Central America, 

 is very constant in color of plumage, but in the moist tropics the following 

 darker colored forms occur : in Honduras, dialeucos; in Venezuela, ridgwayi; 

 in Brazil, braziliensis; and these differ in the amount of pigment in the 

 feathers. By subjecting birds of the northern type to an especially 

 moist atmosphere, Beebe caused them to be so influenced that with each 

 new moulting, whether natural or artificially induced, they always de- 

 veloped darker feathers. Thus a wild bird having pigment in 25.9 per 

 cent, of its area, would have after the second moulting under experimental 

 conditions, 38 per cent, and after the third, 41.6 per cent. Thus during 

 the experiment the typical form assumed the appearance of the three other 

 forms and finally developed plumage markings which have never been 

 seen in nature. Fig. 8 shows the type form, inca, the three geographical 

 variants, and the darkest artificially produced form. 



FIG. 9. Plants of Scilla, started alike but the pot on the right was kept in a dark room. 



(From Ganong.) 



2. Environment Conditions Development of Inherited Characters. 



(a) Light' and Metabolism. In a general sense light conditions life in all 

 normally green plants. It certainly conditions normal development in 

 such plants. Potatoes sprouted in a dark room develop no chlorophyll 

 in the stems and the rudimentary leaves are abortive. In many bulbous 

 plants, however, the influence of moisture and heat are sufficient to 

 induce leaf growth and even development of the inflorescence, but it 

 is all done at the expense of the food stored up in the bulb as is shown 

 in Fig. 9. 



