THE AMERICAN BOTANIST 101 



Dominance of Doubi^e; Fi,owe;rs. — When two different 

 kinds of flowers are crossed, they may indeed produce a com- 

 posite progeny with characteristics of both parents, but usu- 

 ally the first generation resembles one parent to the exclusion 

 of the other. In the new generation, therefore, some charac- 

 ters may appear to be lost, but they are really only latent and 

 appear in the next generation in very definite proportions. 

 When any particular character fails to appear after a cross, 

 we say that it is latent or recessive while those that do appear 

 are dominant. In various experiments in crossing double and 

 single flowers, the astonishing fact is brought out that in some 

 cases doubleness is dominant to singleness; that is, in certain 

 flowers the tendency is to be double rather than single. This 

 is all the more remarkable since flcnvers in the wild are never 

 naturally double. Dominance of double flowers is said to 

 occur in species of Miniulus, Campanula, Althaea, Portulaca, 

 and carnations. 



Color in Portulaca. — The common garden plant 

 known as portulaca or rose moss ranges in color from white 

 and yellow to red or magenta. A Japanese, Kono Yasui, who 

 has been experimenting with the flowers finds that the ma- 

 genta color may be produced by crossing the white and pale 

 yellow flowers. It appears that white flowers possess a 

 generator of magenta pigment (chromogen) but that this 

 fails to act unless stimulated by the pigment of the yellow 

 flowers; hence when white and yellow flowers are crossed, 

 magenta flowers result. Several other pigments are found 

 in the flowers of this species and serve to give them their 

 characteristic colors. There are reported to be two pigments 

 in the scarlet flowers and two others in the deep yellow ones. 

 All the pigments, it may be said, are similar in chemical com- 

 position and differ just enough to make a distinction in each 

 case necessarv. That vellow flowers crossed with white will 



