564 



The \vof)(l cells l\ini,^ between the ducts were still thin-walled and had only 

 half their typical size. In the roots, hoxccver, the outermost zcood cells of 

 the previous annual rimj had not once been thickened. After the tree had 

 blossomed, on the iith of April, investigation still showed no complete 

 termination of the previous annual ring in the roots and not until the 26th 

 of April did the roots become dormant. 



At the time the new annual ring in the branches of the [)re\ious year 

 was alread}- completely lignitied and so thick that six successive ducts coukl 

 be counted in a radial direction in the lowest i)art of the trunk, only a 

 single row of ducts had developed and only the innermost wood cells were 

 found to be thickened. In the main root, the annual ring of the previous 

 year was complete and the cambium already prepared for renewed activity 

 since the bark could be easily separated from the wood body: nevertheless, 

 no traces could be seen of a new wood ring. The bark of the lateral roots, 

 which were as thick as one's little finger, could not be loosened. Thus no 

 complete winter rest was present here. They lingered in this condition 

 until the 30th of April, when some of the leaves were already fully grown 

 and a new wood ring in the main root had begun to develop young, still 

 unthickened ducts. 



We will get an insight in regard to the second of the abo\e mentioned 

 points, i. e., the anatomically different structure of the roots, conditioning 

 a lesser power of resistance, if we bear in mind the time when the annual 

 rings in the trunk wf)uld be developed in contrast to those of the root. 



In the trunk growth, the complete termination of the annual ring will 

 take [dace so much the earlier in the year the higher it is in the tree top. 

 Consequently its development there will consist chiefly of spring wood, 

 lief ore the production of the annual ring has extended to the base of the 

 trunk, summer has come and there is not much more time for the develop- 

 ment of spring wood. Therefore, the diliferentiation of the annual ring 

 must so proceed that (no matter whether it is thick or thin) the relative 

 amount of sprinn ivood to autumn wood decreases from above doi<'nward, 

 i. e., relatixely, the autumn wood increases toward the base of the trunk. 

 This hypothesis has been actually confirmed l)y direct measurements made 

 by v. Mohl', as well as by Hartig- and Sanio''. It should be added here 

 that the thicker the part of the trunk is the higher the maximum of warmth 

 it attains*. 



The firmness of the l;ase of the trunk depends ui)on the predominant 

 formation of autumn wood. 



The character of the tree \ ariety comes into consideration in the devel- 

 opment of the root wood. In conifers, with their early termination of root 

 growth, the dc\elopment falls at a time of greater soil warmth and dryness 



1 loc. cit. 



- loc. cit. 



"■ .Tahrbiicher f. wissen.sch. l?ot. IX, j). 1.55ff. 



■« Ihne. tjiier Baumtempeiatur unter deni Einllus.s der Insolation. Pot. Cen- 

 tralblatt 1883, No 34, p. 234. Vonhau.sen, Untersucliungen iiber den Rindenhrand. 

 All.er. Forst- und Jagdzcitung, X873. 



