GRAVITY AS A FORM-STIMULUS IN FUNGI 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 
XCII 
HEINRICH HASSELBRING 
(WITH THREE FIGURES) 
The directive influence of gravity in determining the position of 
the hymenium in the higher Basidiomycetes is a matter of common 
observation. The fruit-bodies of these fungi are universally oriented 
so that the hymenium is exposed toward the earth’s surface. If the 
normal position of the fruit-body is changed, either by accident or by 
experimentation, readjustment takes place by which the hymenial 
surface is again brought into a horizontal plane, provided of course 
that such readjustment is not hindered by other factors. Interest- 
ing cases illustrating these phenomena are given by ATKINSON’ and 
also by WATERS.’ 
The methods by which the horizontal orientation of the pileus is 
brought about are two. First, in all stalked forms, such as the 
Agaricaceae, and some of the Polyporaceae and Hydnaceae, the 
stalks are negatively geotropic, and by their curvature always bring 
' the pileus into a horizontal position. This property was first observed 
by HormetsTER: in some of the Agaricaceae. The phenomena may be 
observed in all stalked forms growing on the sides of trees or stumps. 
Here the stems curve upward until the pileus is brought into the 
normal position. Second, in forms which have no stalk, and this 
applies especially to sessile forms of Polyporaceae, the orientation of 
the hymenium is brought about by the growth of the trama-plates 
themselves, for, as SAcHs* has shown, the trama-plates of the hymeno- 
t ATKINSON, G. F., Mushrooms, edible, poisonous, etc. pp. 13-17. 
————, Some wood-destroying Fungi. Geol. Surv. of beaibietn: pu 1899: 
333-338. pls. 7. 
2 ee, clr. ne geiaia of Polyporus. Plant World 7:224. 1904. 
ist Ueber die durch die Schwerkraft bestimmten Richtungen 
von Saeed ite Wiss. Bot. 3:92. 1863. 
4Sacus J., Experimental Physiologie. p. 93. 1865. 
251] [Botanical Gazette, vol. 43 
