DISEASES DUE TO SOIL-INFLUENCE 



273 



increased in a few years from O'i86 sq. in. to 2-124 sq. in., 

 and even more. This caused such high tension in the outer 

 periderm that longitudinal rupturing was finally induced at 

 numerous points. Owing 

 to subsequent shrinkage the 

 fissures extended to the wood 

 (Fig. 153, a\ and it some- 



times happened that the 



whole of the cortical tissues 



FIG. 153. Diagrammatic representation of 

 two ways in which the cortex may rupture 

 rate of growth is suddenly 



became detached from the 



wood along the cambium region for some distance on each side 

 of the fissure (Fig. 153, b). The consequence was that the whole 

 of the cortex warped like a board that has been dried on one 

 side. Most of the numerous wounds healed very quickly in 



FIG. 154. Transverse section of the stem of a hornbeam whose cortex had been 

 ruptured in 1876 owing to sudden acceleration in the rate of growth, a, a fissure 

 in the cortex which does not extend to the wood ; b, an occluded fissure ; c, a 

 fissure which has not yet been completely occluded. The figures correspond to 

 the annual rings, these being very narrow in the years 1861 1871. One half 

 natural size. 



about a year, though some not till later (Fig. 1 54), but for a 

 long time the cortex of such hornbeams exhibited an unusual 

 appearance (Fig. 155). 



I have frequently observed the cortex of oaks l to be similarly 



1 Op. tit,, vol. i. pp. 145 150. 



