92 THE HEALING OF WOUNDS 



younger wood may be blocked to a large extent 

 by ingrowths and often by gummy substances, 

 but this does not give complete protection. 

 Moisture is absorbed, oxidation proceeds, and 

 the dissolved organic matter is the beginning of 

 a fertile ground to which wind and rain must 

 bring the germs of bacteria and of our common 

 dead-wood molds. These germs find lodgment, 

 and sufficient moisture for their germination and 

 growth. It is a small beginning, but it is suffi- 

 cient gradually to form a soil more retentive of 

 moisture and full of the products of decay, con- 

 ditions more favorable for the development of 

 wound -rot fungi. 



"From what is known of this matter, it seems 

 fair to assume that bacteria are prominent in this 

 first slow process of weathering; but they are 

 doubtless only secondarily concerned in the deeper- 

 seated injuries where the decay has penetrated to 

 a considerable portion of the trunk. In most 

 cases, they seem to prepare the way for fungi 

 belonging to the toadstool family. One is every- 

 where familiar with these fungi growing upon 

 dead logs or stumps, or even upon the decaying 

 parts of living trees. The fleshy parts which 

 we see are produced at the surface for the pro- 

 duction of the spores or reproductive bodies ; 

 but the truly vegetative parts are usually be- 

 neath the bark or within the tissues, and it is 

 well to note how these develop from the spores. 



