SPORE-DISCHARGE FROM POLYPOREAE in 



photograph. It had started its development on the under side of a 

 branch of a Birch and, in response to the stimulus of gravity, had 

 grown vertically downwards for five years, so that during all this 

 period it had a conical form and was hanging freely in the air from 

 its point of attachment. It appears that in the winter of the fifth 

 year the Birch tree was broken at its base with the result that the 

 long axis of the fruit-body was turned upwards through an angle of 

 about 135, thus taking up the position shown in the photograph. 

 Notwithstanding this displacement caused by the fall of the tree, 

 the fruit-body continued to grow. In the sixth year it produced 

 a hard crust over the mouths of the upwardly directed hymenial 

 tubes and, at the same time, grew downwards at its lower edge so 

 as to form a new horizontal layer of hymenial tubes ; and, in the 

 seventh year, it produced another horizontal layer of tubes. Each 

 new tube of the sixth and seventh years was as perfectly vertical 

 as had been originally the tubes developed during the first five 

 years. 



A consideration of all the above facts justifies one in summing 

 up the relations of a fruit-body of Fomes fomentarius to gravity 

 as follows : (1) the fruit-body as a whole is positively geotropic, for 

 its axis elongates in the direction of the earth's centre ; (2) the 

 hymenial tubes are all positively geotropic, their response to the 

 stimulus of gravity being very exact indeed ; (3) the sterile crust 

 on the exterior of the fruit-body is plagiogeotropic, for it grows 

 downwards at a definite angle with the vertical (it thus allows of an 

 increase in the diameter of each successive annual layer of hymenial 

 tubes) ; (4) each annual tube-layer, as a whole, is transversely 

 geotropic, in consequence of which its under pored surface is remark- 

 ably horizontal ; and (5) the hard supporting and protective crust 

 is formed on the upper side of the fruit-body rather than on the 

 under side, and the naked open tubes which are relatively soft are 

 formed on the under side of the fruit-body rather than on the upper 

 side, as a result of the morphogenic stimulus of gravity. 



The various responses of the fruit-bodies of Fomes fomentarius 

 to the stimulus of gravity appear to be essential for permitting 

 these organs to become efficient producers and liberators of 

 spores. The most wonderful response of all seems to me to be the 



