July, 1920.] 



OGUBA:- GROWTH IN THICKNESS. 



107 



in some cases. Hartig 1 also described the increasing tendency of size 

 of woody elements according to the age in some dicotyledonous wood. 

 I measured the woody elements in Quercus crispula (No. XVI). The 

 wood consists of small and large vessels, tracheid, fibers, parenchyma 

 and rays. Though the change of size of these elements according to 

 the age can be observed very clearly, exact numerical relations are 

 difficult to be given owing to their irregularity. There is an interesting 

 fact in Quercus crispula, that the relative amount of tracheid and 

 wood-fibers in each ring varies according to the age. In the central 

 or younger part of wood, greater amount of fibers developes than 

 that of tracheid, while in the outer or older part the relation is 

 reversed. 



G. Size of xylem-elements of wood 



It is very clear from the above mentioned observations that the 

 size of xylem-elements considerably changes according to age and 

 height. Groom 2 ' 3 and Rushton 2 observed, however, that it may also 

 vary according to the habitat, being greater in the warmer and wetter 

 regions. From these facts, it is very clear that the dimensions of xylem- 

 elements is not constant throughout the wood ; consequently they 

 should not be used as an important diagnostic character for systematic 

 purpose, as has frequently been done by some authors, especially in the 

 work of fossil plants. 



SUMMARY 



1. Thickness of annual rings of trees in succeeding years is not 

 uniform. 



2. Wild-grown trees in the woods have a long young stage of 

 growth in thickness with thin annual rings, and show a very complex 

 type of growth. Many planted trees, or trees growing in open stand 

 are, however, characterized by short young stage of growth in 

 thickness and show a simpler type of growth. 



3. Though radial curves of thickening growth show certain ir- 

 regularities, they may be reduced to a form, which follows the 



4. Hartig, R. (1870) Zur Lehre von Dickenwaehsthum der Waldbaume. — Bot. 

 Ztg, Jg. 28. 



2. Groom, P. and Rushton, W. (1913) The structure of wood of East Indian 

 species of Pinus. — Jour. Linn. Soc. Lond. Bot., vol. 41. 



3. Groom, P. (1914) A preliminary inquiry into the significance of tracheid 

 caliber in Coniferae. — Bot. Gaz., vol. 57. 



