rors] BARTLETT—MASS MUTATION 420 
rigorous experimental methods, might have been overlooked the 
year before. The results from the new F; cultures of 1914 are set 
forth in table I. 
TABLE I 
ANALYSIS OF THE F; SEEDLING CULTURES OF LEXINGTON E 
Culture Seeds Total Forma Mut. Mut. Mut. Mut. 
planted plants typica albicans selacea latifolia graminea 
Spay geen Ss 200* 162 160f ° I (no. 35) |x (no. 36f) ° 
Bw cout 199* 175 172 | (no. 34f) ° ° 2 (nos. 32f 
and 33) 
Ms ee 203* 62 62 ° ° ° ° 
Gee 185* 123 123 ° ° ° ° 
Total 787 522 SLAY I I z 2 
* Indicates seeds from cue opae. 
t 25 plants of f. 
typi t turity, were uniform. The remaining plants of 
f. lypica were discarded in in the rosette stage. 
trek 
4 
It is clear from table I that the F, did not point to Lexington E 
as a specially mutant strain. There were only 5 mutations in a 
progeny of 522 plants. Moreover, 2 of the 4 types obtained, mut. 
latifolia and mut. graminea, were common to the other strains of 
O. pratincola. 
In 1914, F; progenies were grown from 3 plants of O. pratincola 
f. typica belonging to strain E, and the progeny of a fourth was 
grown in 1915. The results are summarized in table II. 
The F, shows a decidedly greater degree of variability than the 
F;. One progeny only, that from Lexington E-5, shows mutations 
in excess of the number of typical plants; the other three progenies 
indicate a degree of mutability more comparable with that of 
certain derivatives of O. Lamarckiana, such as O. scintillans. The 
F,, however, was, if anything, less mutable than O. Lamarckiana 
itself. Successive generations seem to show an increasing degree 
of mutability. Only one F; progeny from f. typica has been studied. 
The parent belonged to the progeny of Lexington E-5, that is, it 
was selected from the most mutable line. The analysis of the F, 
culture is shown in table ITI. 
The salient fact shown by the data for the F,, F., and F; pro- 
genies is that the number of mutations varies inversely with the 
