704 



BRITTLE RACES OF OENOTHERA LAMARCKIANA. 



for Lamarckiana, the results are essentially the same as in the two 

 previous crosses. 



The cross with lata may be compared with the crosses of this 

 mutant with other species, which yield three types of hybrids (3): 

 laeta, velutina, and lata in almost equal numbers (6). From this the 

 expectation for our cross would be: (laeta + velutina + lata) x 

 (laeta + tarda) = laeta x loeta (empty seeds), laeta x tarda (= scin- 

 dens), velutina x laeta (or Lamarckiana), velutina x tarda (= tarda), 

 lata x laeta, and lata x tarda. The last two must reproduce speci- 

 mens of the type of lata. If we calculate these figures on the whole 

 harvest, we get in percentages: 



Counted: 21 barren grains; 36 Lamarckiana + scindens; 16 tarda; 

 27 lata. 



Expected: 17 barren grains; 33 Lamarckiana -{-scindens; 17 tarda; 

 33 lata. 



The conformity of the two groups of figures is quite evident. 



Considering the results of all our crosses, we find that they give 

 proof of the isogamic condition of our new race scindens, and comply 

 with its formula laeta + tarda. In this the laeta gametes do not 

 show any difference from those of 0. Lamarckiana, but the tarda 

 gametes differ from velutina in the absence of the lethal factor. 



Splitting in 0. Lamarckiana tarda. 



About one-third of the seedlings of 0. scindens, reported in table 

 I for 1917, had the low stature and brittle stems characteristic of 

 0. tarda. From one of them I have derived a self-fertilized strain 

 which I cultivated during three further generations and used for 

 some crosses, in order to study its constitution. In these cultures 

 the tarda have split off a new form of the same stature and brittle- 

 ness, but lacking the reddish tinge on the younger parts, and espe- 



Table VII. 

 Pedigree of 0. Lamarckiana scindens mut. tarda. 



