775 



also on the number of the cambial cells. The less the hark pressure, the 

 greater is the number of cell divisions in the direction of the radius of the 

 trunk; the greater also the elongation of the individual cells and ducts in a 

 radial and tangential direction, the lesser, however, in a longitudinal direc- 

 tion. This change in the dimensions increases to such an extent that in 

 those places where the bark pressure is almost entirely removed the thick- 

 walled, elongated wood cells are found to pass over into short parenchy- 

 matous cells. In this, the differentiation of the tissue into cells and ducts is 

 lost. Only a uniform parenchyma zvood develops. 



A work by Gehmacher^ takes up the influence of bark pressure on the 

 structure of the bark itself. His investigations lead to the conclusion that 

 the greater the pressure, the fewer the cork cells formed and, conversely in 

 the same way, the radial diameters of the individual cells differ. The cells 

 of the primary bark parenchyma seem contracted not only radially but also 

 laterally. Their form is, therefore, angular while in those produced under 

 less pressure it is spherical with . considerably larger intercellular spaces 

 (which can disappear entirely under strong pressure). The number of bast 

 fibres is said to increase considerably with a reduction of pressure (which I 

 have not observed myself) and to decrease almost to disappearance with an 

 increase of the bark pressure. 



Nordlinger- also considers the production of a wavy periphery of the 

 wood body, instead of the regular spherical one, to result from bark pressure. 

 Where the wood seems indented the bark frequently appears thicker. The 

 strongly developed groups of stone cells are said to be the ones which are 

 pressed by the bark into the cambium and arrest the growth of the opposite 

 part of the wood. 



If we now give credence to the circumstance to which Kraus'"' calls 

 attention, that part of the cell content is more quickly pressed out from the 

 cell tissue under increased bark pressure, possibly toward those places in 

 which the bark pressure is less, it can be no surprise that a large amount of 

 reserve substances are found stored in the porous parenchyma wood, formed 

 from the cambium as a result of the reduced bark pressure. The wide- 

 lumined, thin-walled parenchyma wood is the most accessible center of 

 deposition for the constructive material flowing toward it. For this reason, 

 we see that where the wood cylinder forms parenchyma tissue instead of 

 prosenchymatous elements, this usually (with the exception of the young 

 callus rolls) is richly filled with reserve substances for a large part of the 

 year and, in fact, in our trees also containing starch. 



All the wounds to the tree trunk bring about a loosening of the bark. 

 Nevertheless, the wood, formed in healing the wound, must vary in structure 

 so much the more from normal wood and take on and retain so much the 



1 Aus Sitzungsl)er. d. Wiener Akad. d. Wissen.sch. Vol. 'LXXXVIir, pt. T; cit. in 

 Botan. Centralbl. 1S83, No. 47, P. 228. 



- Nordlins"ei", Wiikiing- des Rindendriickc.s. Centralbl. 1". d. gesamte Forstwesen. 

 ^Vien. October issue, ISSO, p. 407. 



3 Loc. cit., p. l.SS. 



