8i8 



oped in a way exactly the reverse of that at the constricted place. The cells, 

 bounding the phloem fibres, which in the normal branch are elongated, 

 become considerably broader radially; in fact, they appear Hke long 

 cylinders, lying perpendicular to the phloem fibres; thereby, the overlying 

 bark tissue, which participates less in the radial elongation, is pushed out- 

 ward. Moreover, the rolls, lying between the two constricted places, are 

 not absolutely large ; they are relatively conspicuous only in contrast to the 

 depressions. The secondary bark and the wood follow the convexities and 

 concavities of the primary bark even if with far smaller variations. The 

 pressure, which makes itself felt in the tissues, acts not only where the band 

 lies on the bark but also somewhat above and below the actual place of 

 constriction ; this is seen especially in the cross section of the cells. The 

 mutual proportion in the mean of measurements is : 



In the I-.ark 



Normal Roll Constricted 



Fig. 196, / n Fig. 196, / w Fig. 196, / g 



11,2 11,8 9,4 



In the Wood 



7>3 6,9 4,<3 



Therefore, according to these mean figures which, moreover, show con- 

 siderable fluctuation, an increase manifests itself only in the round and 

 apparently broader cortical cells ; the wood cells, on the contrary, seem some- 

 what narrower than those of the normal wood but it should be emphasized 

 that the same maximum diameter of the wood cells has been found in the 

 roll as in the normal part of the branch at some distance from the constricted 

 place and only the frequency of the occurrence gives the decision. 



If the constriction becomes older, without the band being broken or 

 loosened, as was the case with the wire band shown in Fig. 196, 2 and 5, 

 then the pressure of the wire on the layers of the bark finally increases 

 because of the growth in thickness of the underlying wood in such a way 

 that the bark layers are killed and changed into a brown crumbling mass. 

 Finally, the healthy bark splits above and below the wire and inclosure of 

 the wire begins. Because the overgrowing layers of the annual ring are 

 considerably thicker in wood and bark than at places at some distance from 

 the wire, the former constricted place finally projects in a considerable roll. 



Fig. 196, 4 shows the section, indicated in Fig. 196, 5 at a, considerably 

 magnified. We see here in longitudinal section a little of the old wood of a 

 branch (//) before the wire (d) was bound about it and perceive the new 

 structures of the overgrowth edge at first in the immediate vicinity (U) of 

 the wire and then a continuation of these tissues from the older annual layer 

 (U'). The transitional stages have been omitted for lack of space, likewise 

 the representation of the coalescence, extending about U', of the very 

 uppermost overgrowth edge with the under one and the representation of 

 the transition from the irregularly running wood elements of the overgrowth 



