34 \Yixconsin Academy of Sciences, Arts, and Letters. 



on the elongation growth of young maple trees. He found that 

 the -ivatcst. thickness of each ring normally occurred in the 

 hypocotyledonary or crown region of young trees. The second 

 ring of ihe branches was thicker toward the end than in the mid- 

 dle but subsequent rings decreased regularly toward the distal 

 nid. The third ring of a rather dwarfed, overtopped specimen 

 had its greatest thickness in the three-year-old branches and di- 

 minished toward the base until at the height to which the tree 

 had jjrown by the end of its first year, the ring was almost invis- 

 ible ; at the hypocotyl or crown region and at least as far as 19 

 cm. downward on the roots no growth at all had occurred during 

 the third year. The bark in all cases was thickest at the hy- 

 pocotyl or crown region. 



From the papers cited in this section as well as from others 

 noted elsewhere it is very evident that the distribution of radial 

 growth is at least quite strongly influenced if not entirely deter- 

 mined by the environment and it will be interesting to examine 

 some of the papers in which the factors that have been advanced 

 as being the regulators of this distribution are discussed. 



The publication of Schwendener's 67 epoch-making paper on 

 the mechanical principles underlying the structure of Mono- 

 cotyledons gave a view of plant anatomy from a new angle and 

 still exerts a marked influence on both physiology and anatomy. 

 Many measurements and calculations obtained from typical 

 Monocotyledons are presented in this paper in support of the 

 hypothesis that plant structures take on forms and have the sup- 

 porting tissues distributed in them in such a fashion as to meet 

 the mechanical requirement necessary to make such structures 

 most efficient in carrying their own weight as well as in resisting 

 injurious bending by the wind, etc. In replying to some severe 

 criticism of this paper he 68 admitted that many inaccuracies oc- 

 cur in the calculations but maintained that on the whole it is 

 correct. The general principle developed in the first paper is 

 here also reinforced in its application to Dicotyledons but in a 

 less thoroughgoing way. It was noted that radial growth in a 

 tree-trunk seems to be distributed in a manner so as to meet the 



* Schwendener, S. Das mechanische Princip im anatomischen Ban der 

 Monocotylen mit vergleichenden Ausblicken auf die ubrigen Pflanzen- 

 klassen. pp. 179. 1874. 



8 Schwendener, S. Zur Lehre von der Festigkeit der Gewachse. 

 Sitzungsber. K. Preuss. Akad. Wiss. Berlin. 1884:1045-70. 1884. 



