28 



THE AMERICAN NATURALIST 



[Vol. LVI 



than in tlie {2n-{-l) Globe at the right, which has only 

 one extra chromosome. 



Photographs of capsules (Fig. 7) will further illustrate 

 the idea of unbalance. Unfortunately the {2n + 2) Globe 

 just mentioned fruits poorly and none of its capsules 

 were available when the fruits of the other types were 

 photographed. Later a photograph of a capsule was 

 made to the same scale, and inserted in the proper place 

 in the series. It will be evident that the Globe char- 

 acters of relative stockiness of spines and depression of 

 capsules are more marked in the (2*^ + 2) Globe where 

 there are 2 extra chromosomes in the Globe set than in 

 the + Globe on the left where there is only one 

 extra chromosome in this particular set. Likewise in the 

 modified tetraploids the (plus 2) Globe on the right is 

 more Globe-like than the (plus 1) Globe beside it. 



The degree of unbalance of chromosomes in the nuclei 

 may be given a quantitative expression. Thus in the 

 {2n-^l) Globe, the extra chromosome produces an excess 

 of one over the balanced 2n condition. The nucleus is 

 overbalanced by the active factors in a single Globe chro- 

 mosome. This unbalance may be said to be 1 over 2w. 

 In a similar way the (2w -f 2) Globe with 2 extra chromo- 

 somes has an inibalaiicc ol' 2 over 2h. Having in mind 

 11n->f <|iiaiititaliv.' di tTci'ciiees one would expect the 

 ' <'i"b»' Willi ail unbalance of 1 over 4^ to show 

 n, lc.>> niarki'd cxpiv.s-ion of tlio Globe characters than 

 the {-In - 1) (ilohe with an unbalance of 1 over 2>/. Thev 

 are, in fact, less readily ivcooui/..,! iu recording our ])edi- 

 grees. The relation of unl)alan('e enabled us to predict 

 the possibility of finding (4/^-^2) Globes with an unbal- 

 ance of 2 over hi which one would expect to be as distinct 

 in appearance as {'In + 1 ) Glo])es with an equivalent un- 

 balance of 1 over 2//. The predi<.li(,u lias fullilled 

 and we arc h-d t<. . xp.vt thr app^-a raiicc of (lloh,.^ witli 'J 

 and Globe> wilh 4 .xira nin.n.n.nnu.. in th. (lloU- ..l if 

 tetraploid plants can ciiduiv tli.' cnIivhk^ nnlr. i' A 



