No. 568] X CAPSELLA BURSA-P AST ORIS ARA CHNOIDEA 221 



breeding experiments. On being selfed such a plant 

 should yield : 



It has been shown that plants of the zygotic constitu- 

 tion BBNN and bbNN exhibit the arachnoidea type. At 

 least 50 per cent, of the offspring then should show this 

 character. But if the suggestion made above is the cor- 

 rect one, i. c, that all plants homozygotic for .V exhibit 

 the arachnoidea type, then the parent and its entire off- 

 spring should bear this character. The unfortunate in- 

 fertility of arachnoidal prevents us from submitting this 

 hypothesis to direct experimental proof. But there exist 

 indirect means for establishing the probable truth of our 

 contention. In the first place, we may cross two plants, 

 the identity of which can he established beyond doubt, to 

 wit, attenuata (bbNn) and Treleaseana (BBNn). Such a 

 cross would yield : 



Of these, we would recognize Itbnn because of its rhom- 

 boidea character, 50 per cent, would be recognized as 

 Setchelliana (BbNn), while the remainder, if our surmise 

 is correct, would consist of arachnoidea. Experiments to 

 determine this are under way. At the present we have 

 another, though by far less accurate, means of testing our 

 hypothesis. If the combination NN always results in a 

 form arachnoidea, the offspring of a plant of the zygotic 

 constitution BbNn would be composed of: 



