396 THE AM ERIC AX XATr BALI ST [Vol. LM 



branches and even the main ones under unfavorable con- 

 ditions, or as vegetative growtli slackens, l)eiiig comj^ara- 

 tively small; and we know that organ size also varies 

 considerably in the individual. The point to be empha- 

 sized here is that there tends to be a maximum for the 

 primary diameter of the stem which is attained while the 

 plant is still fairly small, and which thereafter is nor- 

 mally not exceeded, no matter how great the total size of 

 the plant body may eventually become. The same rule 

 applies of course to woody plants, the twigs of a large 

 tree being no thicker, other things being equal, than those 

 of a small tree, although both are usually thicker than 

 the early axis of the seedling. 



Now if the organs (leaves and fruits) (l(>vohii)ed by 

 the primary meristem owe the size wliich they finally 

 attain to the size of the growing point i'vinu which they 

 arise; or if, to put it another way, all tho -tnictures 

 developed at a given growing ])()iTit- the stein axis and 

 the lateral organs — are correlated witli one aiiothfr in 

 size, then the bionietrical results which \vr lia\c set forth 

 in onr bean i>lants are readily ex]»licable. The compara- 

 tively Muall plants are, en this Mippo^ition, the ones 

 which <lid not attain at maturity .Miflicient size to have 

 arrived at the niaximnin >teni ( u'r(»\\ inu- point) diameter; 

 and the snialler the plant-, the sinaller is tlieii" stem diam- 

 etei-, down to depanpei-ate imlixidnal- whose mature 

 ])riniai'\- axes ate no -toutei- than those of the seedling. 

 In these sinallei- plant>, therefore, the significant cor- 

 relation which we observed would naturally be expected 

 between organ -ize (<lepcudent on growing point size) 

 and body >i/.e (delinitely related to growing ])oint size). 

 In the case of the larger ])lants, however (those above 

 the j.oint at wliich the <-ui've of means Hattened out), 

 where the maxininm stem .liametei- or growing imint size 

 has ahvady bc^n attaine.l and wh.T.', the,.. fore, there is 

 no relation between bodv .W.r and -rowin- point Hze. it is 

 only natural that there >honld be (a- ue ..bMM'v.Ml) no 

 correlation at all. I''ui-t lietanore, in the <;-roup of imma- 



