272 



THE AMERICAN NATURALIST 



[Vol. Llir 



alike, or they may be very different from each other. A grain 

 of corn homozygous for yellow starch and red aleurone is dif- 

 ferent in color from one having only one of these characteristics. 

 But to a person vsrith defective vision, or when viewed in a light 

 of proper color, these two colors and a combination of the two 

 may appear to be merely different shades of one color. By 

 breeding this stock with a homozygous white, carrying no con- 

 flicting factors, we should get what would be to this same defect- 

 ive vision a perfect illustration of the behavior of multiple fac- 

 tors. But it is in reality a case of dihybridism in which we have 

 failed to distinguish between the two sets of allelomorphs. And 

 who can doubt that relatively as great a lack of discrimination 

 may characterize our chemical, physical, or morphological vision 

 in observing some of the classical illustrations to which the mul- 

 tiple factor hypothesis is applicable? 



Other examples could be selected from the work that has been 

 done on maize, and doubtless many are available from the inves- 

 tigations made with other plants and with animals, but these will 

 suffice for illustration. Many of the organisms most useful for 

 establishing and testing principles of heredity have an external 

 appearance that may be very deceptive as an indicator of their 

 true structure, and the true structure alone is the key to the 

 deeper significance of their genetic behavior. 



Paul Weatherwax 



ON HETEROPHYLLY IN WATER PLANTS 



The occurrence of two or more different types of leaf upon one 

 individual, which is so fre(iueiitly characteristic of water plants, 

 has long attracted the interest of botanists. The most usual case 

 is that in which the submerged leaves are finely divided while the 

 floating or aerial leaves are relatively simple. Lyte's Herbal 

 (1578) contains a vivid description of this type of heterK)phylly 

 in the water buttercup. Since this description is also noteworthy 

 for its insistence on the influence of external conditions, it may 

 be cited here. 



