8o THE PLANT WORLD 



hence, the possibihty of its reappearance when conditions 

 are right. 



I give below some evidence relating to this question. 



It is confined to three of the most common types of bud 

 variation. In this data, there is but little direct evidence 

 r-s to probable Mendelian behavior in specific cases. There 

 are, however, analogous instances, where the behavior of 

 similar characters after crossing has been recorded. 



Variations in color form over seventy per cent of all 

 bud variations. Color characters have also been the favorites 

 for Mendelian work. They have often been shown to be 

 made up of several factors; but, so far as the writer is 

 aware, presence is always dominant to absence when sap 

 dyes only are considered. The loss of certain color factors 

 could thus account for successive changes of color until 

 entire absence of color is reached. We can, of course, 

 imagine the presence of a factor that excludes the develop- 

 ment of a color potentially present, and by the loss of this 

 factor the color is allowed to form. But this seems unlikely 

 to be often the case. We must, however, note that color 

 phenomena are complex. A dark color may obscure a lighter 

 one belonging to a different allelomorphic pair, when present 

 in the same tissue; and loss of the lighter color would be 

 unnoticed. There may also be different colors present in 

 separate tissues, though they are one in appearance. Such 

 are the yellowish plastids that Bateson (*) has found to be 

 recessive to colorless plastids in sweet peas and stocks. 



\n the tomato, I have discovered four authentic cases in 

 v>'hich a red tomato plant has produced a branch that bore 

 yellow fruit; but I have heard of no instance in which a pure 

 yellow has sported to a red. In this plant Hurst (**) has 

 shown that red is completely dominant to yellow. 



In the potato, bud variation has been almost confined 

 to color variations. Mr. A. W. Sutton (***) makes this 



* Bateson, W. et al. Report to Evol. Com. 3:9. 1906. 



** Hurst, C. C. Mendelian charactOi-s in plants and animals. Third 

 Inter. Con. on Genetic's 114, 1907. 



*** In personal communication. 



