86 College of Forestry 
former upper surface of the fruit-body and on the eighth 
day the transformation was complete. The writer has found 
sporophores of P. pargamenus which had had their hymenial 
surfaces turned uppermost owing to a reversal of the sub- 
stratum. When found the pilei already had enlarged from 
one-fourth to one-half inch in breadth since becoming in- 
verted, the new growth being reversed with respect to the 
position of the old. In other words the original hymenial 
surface abruptly changed to the upper surface of the new 
portion of the sporophore while the original surface became 
overgrown with a hymenial layer. The time required for 
such a change, however, would be but little or no greater than 
that required for normal growth and would vary with the 
climatic conditions. 
It appears then that the stimulus afforded by gravity 
decides not only the direction of the growth of the: pileus 
and hymenial tubes, but also which part of the sporophore 
shall develop and where the tubes are to be formed. In 
other words, gravity acts upon the fruit-body both as an 
orienting and as a morphogenic stimulus. As Buller (1909 ) 
has so ably pointed out in his “ Researches on Fungi,” the 
geotropic reactions enable the hymenial tubes to be developed 
in such a position that, with a given diameter, the maximum 
number of them may be produced i in such a position as to be 
quite protected from rain and that the spores may fall out 
in the easiest possible manner. 
Relation to Light.—A portion of a fallen trunk (three 
inches in diameter) of the wild red cherry (Prunus penn- 
sylvanica Linn. f.) with itumerous sporophores of Polyporus 
pargamenus beginning to make their appearance on it, was 
brought into the laboratory. Two pieces about four and one- 
half inches long were cut from this stem, immersed in water 
for a time, and placed into two glass culture jars. These 
blocks of wood were placed in the jars in the same positions 
with respect to gravity that they occupied in the field. Both 
jars were placed side by side on a table in the laboratory, one 
being covered with a light-proof pasteboard box, and the 
other, kept exposed to the ght of the laboratory, was used 
