1915] BARTLETT—MASS MUTATION 431 
more or less.) The F, progenies of 3 mother plants whose capsules 
contained an average of about 250 seeds gave about 8 per cent of 
mutations, the upper limit of ordinary mutability, as far as experi- 
ence goes. Another F, progeny from a mother plant with about 
110 seeds to the capsule gave over 50 per cent of mutations. Turn- 
ing to the very striking F; progeny, we find that a mother plant 
TABLE III 
ANALYSIS OF F; CULTURES OF LEXINGTON E, FROM LEx. E-5-2209, F. typica 
3 A St 3 FS Sa 
eee eee gece 3 32 
Culture a 4 = s 3 8 3 Other mutations = 2 3 
a/3|/8lelelaels 32 | 82 
w = & = a = = = As 
ao cae 39 30 O12¢9 I I 19 | 0 21 | 70 
Be ee oe 86* | 56 ors 4 4 39 | 1 (angustifolia)| 50 | 89.3 
teat 3 is a 3 8 43 4 | 76.1 
FR ager a 100" | 44 22,150 = 5 42 | 2 (gigas?) 52 | 70.3 
Shee SO" F468 to 2047-3 3 4 18 | 0 28 | <8.3 
OC a O77 | 0G) 24.0 4 2 39 | oO 45 | 65.2 
(Loe Oe" 1. Se Tip 1 6 3 I 28 | 0 ‘ 32 | 62.7 
Biases toa" | oe bas eto 4 3 Aa} (2) 5O\) 95.2 
Gani. TOS” | 68 { a0l1. ce 3 ° 45. )0 38 | 55.9 
5 fo ee 142* | 102 Se Ba ° 5 89 | © 04 | 92.2 
GS Ree 50°. 1.30 yee 5 2 28} 0 35 | 89.8 
Sta SNC! oP 1 O61 44 Lo 5 3 43 | I (gigas?) 52 | 80.0 
Pu, 83* | 65 rN Gee 4 6 46) 0 57 | 83.7 
BA ey Ssh Paes TEs ° I 22°16 aa 1 67.3 
: oe ne Th Oa ns a ee 6 2 30,0 40 | 67.8 
cs RE eR ee 990 SE) Eee St 7 2 26 | 0 36 | 70.6 
shy ekg ty O71. 73 1 te 1. 8 2 5 5319 60 | 82.2 
Total. .| 1477 |1036 | 266 | 10 | 57 | 54 | 6441 5 770 | 74.3 
_ *Seeds from one capsule; the entire progeny was classified from the young seedlings; 30 plants of f. 
typica and all the mutations except the weaker individuals of mut. sefacea were retained. 
with only go seeds to the capsule gave almost 75 per cent of muta- 
tions. It would be necessary to have much more complete data 
to establish any exact relationship between progressive sterility 
and mutability. Nevertheless, it is beyond question that the 
decrease in the number of seeds has gone hand in hand with the 
increase in mutability. 
In Ocenothera pratincola, therefore, the phenomenon which I 
have termed mutation en masse is associated with the failure of a 
