168 University of California Publications in Zoology. [Vol.6 



Examining farther, we find in the plant world what seems to 

 be a parallel to segmentation in the chain. Quoting again 

 (Pfeffer, '03; vol. II, p. 6) we find: "In flowering plants, the 

 embryonic cells form the leaf-primordia and hence determine the 

 number and position of the appendicular organs, which attain 

 their adult shape by subsequent growth." 



But there is a possibility that the phenomena we are studying 

 should be compared rather with another phenomenon of plants 

 called by Moll 4 the "Langenperiode der Internodien. " This 

 relates to the widely observed fact that the internodes of a grown 

 branch vary in length and that the differences in length are found 

 to follow a certain order. 



Results of quantitative investigations on this subject are given 

 in a paper, "Die Periodicitat morphologischer Erseheinungen bei 

 den Pflanzen." (Tine Tammes, '03.) We find in this paper the 

 following statement, "Betrachtet man die Stellung der Laub- 

 blatter an einer Pfianze etwas niiher, so wird man bei vielen 

 Pflanzen die kleinsten Blatter an der Basis und an der Spitze, die 

 grossten in der Mitte finden. Audi bei den Seitenzweigen tritt 

 dieselbe Erseheinung auf, die zuerst gebildeten Seitenzweige sincl 

 kurz, dann folgen langere und auf diese wieder kiirzere. Die 

 ganze Pflanze zeigt ein Bestreben anfangs kleinere Organe zu 

 bilden, spater grossere und gegen das Ende ihres Lebens wie- 

 derum kleinere." 



Observation of plants shows this scheme to hold true in large 

 numbers of cases. We see it in the shape of the leaf, in the size 

 of the leaves on a branch and in many cases in the sizes of the 

 branches upon the main trunk. It is especially noticeable if one 

 compares the size of the leaflets of a series in many compound 

 Leaves. The distances between the leaflets of a series, and between 

 the leaves of a branch also bear certain definite relations. The 

 leaves on a young tree will be found to be closer together at the 

 base and tip than near the middle. This much we can see, but 

 just what these relations are, whether they are the same for all 

 the branches of a tree, young and old, and the same for all trees 

 of a species, and whether another definite relation holds true for 

 all leaves on a branch, those at the base, middle and tip, or 



* I have not, unfortunately, had access to Moll 's work, but know it 

 chiefly through Tamme's paper. 



