496 
J. G. GROSSENBACHER 
through the dormant season in immature condition, and thus are 
Hkely to become injured. NordHnger^ found by peeHng tests that 
cambial activity precedes cortical growth and may continue after 
cortical growth ceases. In some cases, however, cortical growth 
continued later than cambial activity. 
R. Hartig^*^ describes several cases in which the bark of a very 
high percentage of forest trees was burst and injured at certain 
places two years after those forests had been thoroughly thinned. 
After thinning, the trees grew as much in one year as they had grown 
before in many years. His conclusion, that the bark burst in early 
summer owing to the rapid radial growth of the wood, can fortunately 
be more carefully examined because he gives a photographic record of 
cross-sections. These figures prove beyond question that the bark 
was split and separated from the wood during the dormant season 
preceding the growing season in w^hich he assumes the splitting to 
have occurred. From Fig. 52, Plate XXVII, which is a reproduction 
of one of Hartig's figures, it is apparent that the bark injury occurred 
between the growing seasons and not while growth was going on 
because the lines of injury and separation coincide with the line 
separating the wood of two growing seasons. Another case which 
Hartig gives in some detail, in which a high percentage of the trees 
in a thinned forest sustained bark injuries just above or at the ground 
line a few years after thinning, is also of decided interest. In this 
instance he concludes that the rank growth of herbaceous plants 
developing about the tree trunks after thinning prevented proper 
aeration, excluded light, and thereby injured the bark. But in this 
case as in the former, cross-sections show that the injury occurred 
during the dormant season, when aeration was probably good. The 
chief difference between these two cases lies in the fact that in the 
former instance the tension reached a high enough point to rupture 
the bark as well as to loosen it, while in the latter the tension was 
less. It seems possible that in one instance the bark was more 
resistant to radial rupture than in the other, though it is likely that 
some additional factors are involved in the occurrence of radial clefts. 
^ Nordlinger, H., Wann beginnt Bast, wann Lederschicht der Rinde sich zu 
lozen? Centralbl. Gesamt. Forstwes. Wien. 5: 128. 1879. 
Hartig, R., Zersprengen der Eichenrinde nach plotzlicher Zuwachssteigerung, 
Untersuch. Forstbot. Inst. Munchen i: 145. 1880. 
, Das Zersprengen der Hainbuchenrinde nach plotzlicher Zuwachssteiger- 
ung, Untersuch. Forstbot. Inst. Munchen 3: 141. 1883. 
