﻿BOTANICAL GAZETTE 



A. alba Bigelow 

 Berries milk white, tipped with 

 red, smaller, about 8-seeded, 

 on short, red, incrassated filiform pedicels, one-fourth 

 pedicels as large as the com- as large as the common 



Flowers a week or two later 



To the differences mentioned on p. 193 we may add therefore 

 (1) greater pubescence of the raceme in A. rubra, and (2) filaments 

 nearly twice as long as in A. alba. Differences which I have not 

 verified are (3) berries of A . rubra with about twice as many seeds, 

 (4) petals more numerous, and (5) sepals green instead of white. 



From these facts it is clear that the differences between A . rubra 

 and A. alba are numerous and affect the fundamental structure of 

 the plant. It becomes a question whether all of these differences 

 could be determined by only two mutations, and this is a matter 

 on which only breeding experiments can throw any light. Of 

 course, it is possible that the quantitative decrease in the pubescence 

 of A . alba may be correlated with the increase in thickness of the 

 pedicels, both being structural expressions of the same inner 

 germinal change. Similarly, it is possible, although perhaps 

 scarcely probable, that such changes as smaller size of berries, lack 

 of pulp, larger and fewer seeds, and truncate petals in A. alba are 

 all aspects of the same change which made the berries white. The 

 minor differences in shape of berries and leaves have also to be 

 taken into consideration if they are not mere fluctuations. 



The frequent occurrence of such vanishing distinctions as those 

 just mentioned affords one of the main difficulties of taxonomic 

 work, and the presence of the "residua" of characters in super- 

 posing one species upon another has been thought to offer serious 

 difficulties in explaining the origin of one species directly from 

 another. A careful examination of known mutations, however, 

 shows that similar conditions occur here. Thus, in Oenothera 

 brevistylis the main distinctions from O. Lamar ckiana are in the 

 very short styles and sepal tips and the misshapen stigmas. But 

 minor differences of a quantititave sort are found throughout the 

 plant, notably in the more obtuse tips to the leaves, a feature which 

 shows quantitative variation in the foliage of each individual. 



