750 Forestry Quarterly 



pressure requires ; and in extraordinary storms they, too, succumb, 

 so that their claimed inherited structure through selection is of no 

 advantage to them. The author then adds arguments demolishing 

 Metzger's theory. He believes to have proved that a bending 

 force according to its intensity produces quite varying reactions; 

 even where no bending due to exterior pressure exists, increased 

 increment takes place, as on the concave places of a branch or 

 root ; if the shaft were the product of wind pressure, then the tree 

 form would have to vary from locality to locality, like the local 

 winds ; trees woiild rarely have concentric form and regular struc- 

 ture; either the form is the mechanical product of the present wind 

 direction, when there would be no inheritance effect; or the 

 present form is the result of natural selection and inheritance, 

 when there would not be reaction to present winds. The author, 

 then, brings forward his theory that the form is a result of condi- 

 tions of nutrition and especially of water conduction. 



Since air and light (diffuse, which is the important part in 

 assimilation) surround the crown symmetrically, hence the shaft 

 must assume a symmetrical radial structure (just as in sea anem- 

 ones, corals, etc., which live surrounded by equal feeding chances 

 on all sides) . In the horizontal branches gravity produces eccen- 

 tricity. 



To secure uninterrupted water conduction a conduction layer 

 is required which is in proportion to the transpiring organs, such 

 a layer is represented by the area of the vessels and tracheids of 

 the last three or four annual rings at any cross section. 



To preserve equality of conducting area, it would be necessary 

 to have an increasing ring width towards the crown on account of 

 the decreasing circimiference. Asstiming that this conducting 

 area will be proportional to the ring area, the author calculated 

 the form which a spruce would have to assimie to become a shaft of 

 equal water conductivity, and found very satisfactory agreement with 

 actual forms. 



A figure illustrates the method of calculating and the resulting 

 form, also showing that Metzger's theory will not hold. 



Microscopic investigations of the last rings of several spruces 

 and firs show a minimum of ring area at a height several meters 

 above ground, and from this point an increase of ring areas toward 

 base and crown. A relative thickening of the shaft above the 

 lowest dry branches was also found a common occurrence, evi- 



