| 
| 
1907] HASSELBRING—FORM-STIMULUS IN FUNGI 255 
differentiation is independent of the external stimulus of gravity, 
but the general form of the plant is somewhat modified in a way to be 
considered later. In the highly differentiated Coprinus the morpho- 
genic influence of gravity is not evident. 
The sporophores of all the higher fungi are made up of a complex 
mass of hyphae whose growth is so correlated that the final result is 
the definitely organized fruit-body. These hyphae must be con- 
sidered to a large extent as independent individuals, for they have 
organic connection only in so far as they arise from common branches 
many cell generations. back in the tissue, or in so far as they are 
united by subsequent fusion which is comparatively rare. The 
elements, nevertheless, grow in unison to form the sporophore. As 
the organization of the sporophore is in the main the result of 
successive changes in the direction of growth of elements,° it seemed 
possible that this mode of growth might be determined by external 
stimuli, coupled of course with a changing capacity of the elements 
for reacting to those stimuli. For example, if gravity alone were 
considered, the hyphae organizing the pileus of mushrooms might be 
plagiotropic while forming the cap, those on the lower side becoming 
positively geotropic to organize the lamellae, while the hyphae organiz- 
ing the hymenium would again be plagiotropic. Of course it is not 
supposed, and the experiments bear this out, that any case would 
yield to so simple an analysis as this, for it is still possible that the 
plant has within itself an inherited tendency toward a definite organi- 
zation, and even if this is not admitted the common chemotropic and 
thigmotropic actions of the hyphae upon each other play an important 
part. That direct external stimuli also play an important part is 
shown by the non-development of Lentinus lepideus? in the dark. 
The caps of some species of Coprinus® also are dependent upon light 
6 Arkinson, G. F., The development of Agaricus ey Bor. GAZETTE 
42:241-264. pis. 6. 1906; the older literature is reviewed h 
ALLEN, C. L., The development of some species of Hiegieision: Ann. Myc. 4: 
387-394. pls. 3. 1906. 
7 REINKE, J., Ueber Deformation von tenes durch dussere Einfliisse. Bot. 
Zeit. 62:81~112. pl. 1. aoe see the literature given 
Butter, A. H. R., The reactions of the aie of Lentinus lepideus Fr. to 
external stimuli. tat of Botany 19:427-438. pl. 4. 1905. 
8 BREFELD, O., Untersuchungen iiber Schimmelpilze 3:87-97, 114-115. 1877. 
