480 



SCIENCE 



[N. S. Vol. XXVI. No. 667 



necessary for the tree to attain the age at 

 ■whicli it has heartwood before it may become 

 infected by this f un^s ; that is, it seems to be 

 necessary that the tree shall have heartwood 

 and that the heartwood must be exposed by 

 some injury before Fomes Bihis is able to 

 obtain an entrance to its trunk. While there 

 is a bare possibility of exceptions to this rule, 

 no such were found. Practically every tree, 

 in which wounds were found by which the 

 heartwood was exposed, was infected and bore 

 one or more sporophores of the fungus. 

 Fomes Bihis enters the trunk of the tree ap- 

 parently in the same manner as do most of 

 the so-called " wound parasites." It obtains 

 a foothold in one of these injuries and gradu- 

 ally progresses into the heartwood of the stem ; 

 once entrance has been obtained to this, the 

 rot gradually extends upward, downward and 

 sidewise from its first entrance into the trunk 

 until the tree finally dies or is broken over by 

 the wind. Wlien the heartwood has become 

 completely affected through its entire thick- 

 ness, the adjacent rings of the sapwood seem 

 to prematurely assume the characters of 

 heartwood, and the rot finally extends into 

 them also ; so that in extreme cases the sap- 

 wood is found to be even thinner than it 

 normally is. Cases were found where this 

 process apparently extended until the tree was 

 killed outright. A number of other cases were 

 also found in which but a single ring of the 

 sapwood still remained alive. 



The heartwood of Sassafras is normally of 

 a rather dark brown color, but when attacked 

 by this fungus it assumes a slightly redder and 

 lighter color. This color of the rotted wood is 

 undoubtedly due to the fact that the mycel- 

 ium of this fungus is itself of a ferruginous 

 brown color, and thus helps to give a brown 

 coloration to the tissues within which it is 

 located. The wood is very porous, and the 

 fungus fills the large vessels and tracheids 

 with its brown mycelium, forming tangled 

 masses which completely fill their cavities. 

 Between the healthy and the rotted wood is 

 a narrow black zone. Microchemical tests 

 indicate that the fungus does not exert a very 

 active delignification upon the cell walls, but 

 that the tendency seems to be for a more or 



less complete local solution of the entire cell 

 wall. The rotted wood seems to retain much 

 of its original appearance, yet has been very 

 decidedly weakened by the action of the fungus 

 in dissolving the middle lamellse from between 

 many of the cells, so that they adhere to each 

 other but slightly. Perley Spaulding 



Laboeatort of Foeest Pathology, 

 U. S. Department of Ageiculturb, 

 Washington, D. C. 



note on the movement of moisture in soils 

 In teaching physics it is particularly im- 

 portant, whenever practical, to show how phe- 

 nomena observed in nature are explained by 

 facts discovered in the laboratory. For this 

 reason it is hoped that the following, though 

 containing nothing new in physics, may be of 

 interest to those who have the honor of in- 

 structing others. 



It is known that evaporation, condensation 

 and surface tension, all play important roles 

 in the movement of moisture in soils. The 

 U. S. Department of Agriculture has con- 

 ducted a number of investigations on these 

 subjects, and has reached some valuable con- 

 clusions. The effects, however, due to changes 

 in surface tension, produced by changes in 

 temperature, have not been considered in de- 

 tail, nor do I recall having seen them men- 

 tioned anywhere else. 



It has long been known that the surface 

 tension of a liquid increases as its tempera- 

 ture is lowered. In the case of water at least 

 this relation continues at the same rate to and 

 below the ordinary freezing point, provided 

 the liquid condition is maintained; and there- 

 fore any change in the temperature of the soil, 

 such as takes place to a greater or less extent 

 every day and night, mvist produce a corres- 

 ponding movement of its moisture towards' the 

 colder parts, where the surface tension is 

 greatest. Besides, evaporation, which is most 

 rapid where the temperature is highest, and 

 condensation, which is greatest on the coldest 

 surfaces, produce moisture movements in the 

 same direction as those made by temperature 

 changes in surface tension, so that the several 

 causes work together. But, owing to a variety 



