ll(i Shull. 



l)ecte(l and the actual numbers in the Fo from the new crosses is much 

 closer than in the original Fo, largely due, I believe, to the fact that 

 we have continued to learn how best to meet the cultural requirements 

 of the plant. In the recent cultures nearly every individual could be 

 classified, while in the earlier cultures the plants became diseased after 

 growing loug under unnatural conditions, and many died unclassified. 

 Our present interest lies in tlic fnM|ueucy of occurrence of tho two 

 kinds of capsules: tiie rosette- characters are given in the tal)le 

 only for tiie purpose of completing the parallel with the previously 

 published results of the original Fs. The,v serve, however, to demon- 

 strate again the complete independence of the capsule-characters from 

 the leaf-characters. It is seen that, with respect to the capsules in all 

 four families of the new Fs, the agreement with the monohybrid i-atio is 

 striking, whereas tlic original Fa showed in each family an approximation 

 to the ratio 1.5 : 1. 



Discussion. 



We have seen that considerable departures from the expected 

 ratios have appeared in many of the families, and yet, that in every 

 trst The essential features required by the assumption that there are 

 two inde])en(hMit determiners for the triangular capsule have been 

 strikingly manilcst. I take it. tliercfore. that this hypothesis must be 

 in a general way conTct, although the deviations in the ratios iiave 

 raised other (|ucstioiis wiiich will need still further investigation for 

 their definite solutieii. 



Tlie deviatiiuis IVoMi the ex])ected ratios chanced in F- and F:i to 

 lie all in tlie same (brection, indicating in every family a deficiency in 

 tlie iiumlier 111 individuals of tiw Hi'egeri type, and two hypotheses were 

 suggested (StiULL 1911) as possibly accounting for tliis condition, namely, 

 (a) that B. Heegc.ri is a constitutionally weaker type and that in con- 

 sequence there is a differential elimination of plants of this tyjie; or 

 (1)) that there is a selective mating in which the union of unlike gametes 

 is favereil. 



In the j-'i ;iii(l 1"":,. lio\ve\('r. the Heei/cri plants have been in excess 

 of expectation about as frequently as they have been deficient. This 

 result miirht seem to disjjose of the first of the two liypothes(>s, — the 

 line wliicli 1 tliiiiiiiiit the MKnv |ii'iili;ililr. Idi' if the J/eryoi type were 

 much wt'.akei' at an early stage of its de\elopuieut, than the hursa- 

 postoris type, we might expect that there would always be a deficiency 

 in the number of Heegrri plants reaching maturity. This would be an 



