6i9 



of discoloration are visible in the collenchymatous outer layer of the bark 

 but may be found in the pith crown, which appears to be entirely brown. 

 This browning decreases with the distance towards the heahhier base of 

 the branch at which the sections were made. At the base of the branch 

 we find only scattered cells, with yellow, swollen contents. 



A difference in direction of the holes thus produced becomes noticeable 

 in the abundantly recurring cracks. Within the pith disc may be found 

 the greatest radial extension of the holes which is seen to be connected with 

 a pecuUar, radiating formation of the pith. This is found to be distended 

 into a pentagon, produced by the passing of the vascular bundles, com- 

 posing the wood ring, out from the wood ring. As indicated above, the 

 cause of this extension of different bundles lies in the fact that, in each of 

 the five corners of the pith, the vascular .systems, destined for the five next 

 higher leaves, are about to make their way outward through the bark into 

 the leaves. The pith body for the leaf lying next above the part of the 

 branch here illustrated, is naturally furthest distended and is adapting itself 

 to passing over, as a pith connection (mb), into the next bud. The bundles 

 of the two higher leaves, lying only one or two internodes above the place 

 of the cross-section, still lie within the complete wood ring, but even they 

 have already formed noticeable distentions of the axial cylinder (at the right 

 in the figure). The bundles for the 4th and 5th leaves, following the spiral 

 of the leaf insertion, still lie entirely within the wood ring and indicate 

 their lateral appearance only by a slight outward convexity (at the left side 

 of the figure). Between them the pith body is continued only in the form 

 of a broadened medullary ray and has not widened into an actual pith 

 connection. 



The holes (/), produced by the rupturing of the tissue, correspond in 

 size to the amount of distention of the pith. The larger these are, and the 

 nearer they stand to the buds belonging to them, the stronger is the radial 

 splitting. Differing from those in the pith, we find the holes (/') in the 

 bark extending tangentially. They are produced, in part, by the throwing 

 off of the peripheral collenchyma of the parenchyma, rich in chlorophyll, in 

 part, however, by the rupturing of individual parenchyma cells. It should 

 be noticed, that the formation of holes in the bark, as also the formation of 

 thin-walled tissue (ph-lg), is much greater on the side of the branch where 

 the bundle has separated most widely from the main vascular system than 

 on the opposite side. Moreover, this also explains the fact that, in the 

 investigation of branches injured by frost, as a rule, one side is found more 

 greatly affected than the other. The natural conclusion, that the action of 

 the frost has been greater on one side is usually erroneous. For, if a num- 

 ber of successive internodes are examined by series of sections, the investi- 

 gator will be convinced that sometimes one side of the same branch shows 

 a greater injury from frost, sometimes the other, according to the position 

 of the bud, near which the section was made. The closer to the bud, the 

 stronger the action of the frost in the branch. 



