rots] 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 Jies 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 O. pratincola f. typica, with a much-branched terminal 
inflorescence; fruiting freely by self-pollination and producing a normal 
UAE OF VIMTNE MORON in os cache eee es mut. formosa 
_ Plants — Psa leaves whitish, broader and thicker than in the last; 
ple and bearing a few thick-tissued, usually cleistogamous 
tlowers; ie by self-pollination large, apparently normal capsules 
Wren COntaln Very TEW BEOUS 2 Sec cee ee 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-pollination and only shriveled capsules with few 
Hobcs Dy artificial GOUMIAHON Sos ok ae re i ec ok aes mut. revoluta 
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. selacea 
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 
