I9I5] 



BARTLETT—MASS MUTATION 



431 



more or less.) The F2 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 

 1 10 seeds to the capsule gave over 50 per cent of mutations. Turn- 

 ing to the very striking F3 progeny, we find that a mother plant 



TABLE III 

 Analysis of Fj cultures as Lexington E, prom Lex. £-5-229, r. typica 



Culture 



a 



o 



Other mutations 



^2 



P 



2 



3 



4 



S 



6 



7 



8 



9 



10 



II 



12 



13 



14 



IS 



16 



17 



Total. 



39^ 



86* 



91* 



100* 



80* 



97* 



95* 



104* 



105* 



142* 



59* 



79* 



83* 



85* 



72* 



73' 

 87* 



30 

 56 

 71 

 74 

 48 

 69 

 51 

 73 

 68 

 102 

 39 

 65 

 65 

 42 



59 



■51 

 73 



9 

 6 



17 



20 

 24 

 19 

 21 



30 

 8 



4 

 13 



8 

 18 

 19 

 15 

 13 



19 

 39 

 43 

 42 

 18 



39 



28 



44 

 35 

 89 

 28 



43 

 46 

 22 



30 

 26 



53 



I 



o 



2 (gigas?) 



o 



o 



o 



l(?) 



I {gigas ?) 



o 



o 



o 



21 

 50 

 54 

 52 

 28 

 45 

 32 

 52 

 38 

 94 

 35 

 52 

 57 

 24 

 40 



36 

 60 



70 

 89 

 76 

 70 

 58 

 65 

 62 



71 

 55 

 92 

 89 

 80 

 87 

 57 

 67 

 70 

 82 



1477 



1036 



266 



57 



54 



644 



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. selacea were retained. 



with only 90 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 mutabihty. Nevertheless, it is beyond question that the 

 decrease in the number of seeds has gone hand in hand with the 

 increase in mutability. 



In Oenothera pratincola, therefore, the phenomenon which I 

 have termed mutation en masse is associated with the failure of a 



