igisl BARTLETT—MASS MUTATION 427 



The characteristic mutations of the mass mutating strain 



The four mutations, which by occurring in such large numbers 

 characterize the hereditary behavior of Lexington E, form a group 

 with a common structural peculiarity which sets them apart from 

 typical O. pratincola and from all the other mutations. This 

 peculiarity lies in the narrow, strongly revolute, veiny leaves, of 

 which the midrib is frequently but not always prolonged from a 

 point below the apex as a setiform appendage. This appendage 

 strongly resembles the infra-terminal calyx tips of certain species 

 of Oenothera, and suggests the translocation of a character from 

 one organ to another which does not typically display it. The seti- 

 form appendage is exceptionally a centimeter long but is entirely 

 absent on some leaves of each individual mutation. It may be 

 said that the four mutations are characterized by the possibility 

 of manifesting the appendage under favorable conditions rather 

 than by its invariable presence. The revoluteness, narrowness, 

 and venoseness of the leaves, however, are characters which are 

 always distinctive. 



The four characteristic mutations may be contrasted as follows: 



Plants as tall as 0. pratincola f. typica, with a much-branched terminal 

 inflorescence; fruiting freely by self-pollination and producing a normal 

 number of viable seeds mut. formosa 



Plants semi-dwarf; leaves whitish, broader and thicker than in the last; 

 inflorescence often simple and bearing a few thick-tissued, usually cleistogamous 

 flowers; producing by self-pollination large, apparently normal capsules 

 which contain very few seeds mut. albicans 



Plants semi-dwarf; leaves green, narrower than in mut. formosa; inflores- 

 cence densely branched and many-flowered; ovaries almost sterile, producing 

 no capsules by normal self-poUination and only shriveled capsules with few 

 seeds by artificial pollination mut. revoluia 



More extreme dwarfs, with narrowly linear leaves; inflorescence-bearing 

 branches with broader leaves than the rest of the plant, simple, with thick- 

 tissued, usually cleistogamous flowers which produce large normal fruits but 

 very few viable seeds by natural self-pollination mut. setacea 



The four mutations do not form a linear series showing succes- 

 sive degrees of reduction. Mut. formosa and mut. revoluta are 

 very similar and might be interpreted as successive reduction stages. 

 They differ in size and fertility, but have many morphological 



