30 BULLETIN 275, U. S. DEPARTMENT OF AGRICULTURE. 



and the species of wood on which, for instance, a fungus like Echino- 

 dontium tinctorium (Indian-paint fungus), the most common de- 

 stroyer of white-fir heartwood, can exist, its growth will still be 

 dependent on the presence of heartwood of a certain character and 

 on the water content of the heartwood. This is evidenced by the 

 fact that decay is so commonly found in concentric development at a 

 certain distance from the sapwood. The heartwood contains water 

 in varying degrees, although it does not lift water like sapwood. 

 But there is nothing surprising or irrational about the assumption 

 that the water content of the heartwood will depend more or less 

 on the water movement in the sapwood. The water in the heart- 

 wood of conifers is found in the membranes of the tracheids, not in 

 the lumina. In a normal sound tree, heartwood of a given age and 

 diameter surrounded by sapwood of normal width, corresponding to 

 a certain crown development, will contain approximately a standard 

 amount of water. Decrease in crown activity through some cause 

 or another (suppression, injury to the crown, etc.) will soon be 

 expressed in a rapid progress of heartwood formation, leaving only a 

 narrow strip of sapwood, through which very much less water will 

 move upward to the crown than in the normal tree. We may safely 

 assume that the water content of the heartwood will change to a 

 certain degree with the amount of water moved upward in the sap- 

 wood. The water content of the sapwood changes, furthermore, 

 with age, and also with the season. Both changes must also appear, 

 although in a far less degree, in the heartwood. Munch 1 has em- 

 phasized, in a series of very interesting papers, the relation of wood- 

 inhabiting fungi to the water and air content of the host tissues. 

 Water-logged tissues are inaccessible to these fungi; a certain mini- 

 mum of air, as Munch expresses it, must be present in the tissue in 

 order to allow the development of the hyphae. 



Variations in the water contained by imbibition in the cell mem- 

 branes must influence the degree of humidity of the air in the lumen 

 of the cell itself; it is quite probable that this factor also plays a role 

 in the distribution of hyphae in the wood. 



What percentage of water in the cell membranes and of air in the 

 lumina of the heartwood presents the optimum for the development 

 of Echinodontium tinctorium and other similar fungi we do not know; 

 but evidently there must be an optimum, a maximum, and a mini- 

 mum. Any factor influencing the quota of water and air in the heart- 

 wood must, therefore, be of great importance. Cracks in the sapwood 



i Munch, Ernst. Die Blaufaule des Nadelholzes. In Naturw. Ztschr. Land- u. Forstw., Jahrg. 5, 1907, 

 Heft 11, pp. 531-573; Jahrg. 6, 1908, Heft. 1, pp. 32-47, 33 figs.; Heft. 6, pp. 297-323. 



Munch, Ernst. Untersuchungen fiber Immunitat und Krankheitsempfanglichkeit der Holzpflanzen. 

 In Naturw. Ztschr. Forst- Land u. w., Jahrg. 7, 1909, Heft 1, pp. 54-75, 5 figs.; Heft 2, pp. 87-114; Heft3, pp. 

 129-160. 



Munch, Ernst. Uber krankhafte Kernbildung. In Naturw. Ztschr. Forst- u. Landw., Jahrg. 8, 1910, 

 Heft 11, pp. 533-547; Heft 12, pp. 553-569, 2 figs. 



