32 INTRODUCTION [CH. 



On the other hand Stevens and Hall found that the pycnidia of Phyllo- 

 slicta sp. were irregularly scattered in continuous darkness but developed in 

 regular concentric zones when exposed to the alternation of day and night; the 

 rudiments of the pycnidia in this case are laid down mainly during the night. 



Geotropism. The influence of gravity has been very inadequately studied 

 among the lower fungi, little having been done since Sachs, in his Lectures 

 on the Physiology of Plants in 1882, described the sporangiophores of Mucor 

 and Phycomyces as bending up and the rooting hyphae down; he worked 

 with filaments extending in all directions from a suspended piece of bread. 

 Kny in 1881 reported that the mycelia of Mucor Mucedo and Rhizopus nigri- 

 cans and also that of Eurotium repens are indifferent to gravity, and Miyoshi 

 denied any geotropic reaction in his fungi. 



Dawson in 1900 found that the stromata of Poronia punctata, a copro- 

 philous pyrenomycete, show a well-marked negatively geotropic reaction 

 from the earliest stages of their development and the same will probably 

 prove true of other forms with upright stromata or with stalked fructifications 

 like the Helvellales and many Pezizales. 



Among the Hymenomycetes negative geotropism was first recorded by 

 Sachs in i860, and soon after by Hofmeister in 1863. In stipitate forms the 

 stalk is always negatively geotropic as soon as the pileus develops, though, 

 in some of the Coprini and in Lentinus lepideus, this may be preceded, as 

 already seen, by a phase in which light is the directive influence. 



Buller in 1909, and Streeter in the same year, showed that the geotropic 

 response is of the nature of a gradual adjustment. The growing stalk swings 

 beyond the vertical line, changes its direction and swings across it again, 

 passing the vertical two or three times before it comes to rest. Curiously 

 enough this method is followed in Amanita crciiu/ata, in which the stalk 

 reaches its full development in twenty-four hours, although there is not time 

 for a complete adjustment, and the sporophore often comes to rest beyond 

 the vertical line. The young stipe in Amanita elongates throughout its 

 length until more than half grown ; the zone of most rapid elongation is just 

 below the pileus, it finally becomes narrower and narrower until growth 

 ceases. Streeter was able to locate the perceptive region in the stipe, 

 not in the pileus. Amanita showed a definite geotropic response when 

 placed in a horizontal position for only one minute before being rotated on a 

 klinostat. When stimulation lasted for a shorter period (13 or 30 seconds) 

 no upward curvature ensued but a spiral curve was formed in the direction 

 in which the klinostat moved. The latent period of young, vigorous 

 specimens is about 40 minutes. 



In the stemless Hymenomycetes, as in the stipitate forms, the orientation 

 of the pileus takes place in response to gravity. This may be seen on any old 

 stump where the bracket-shaped species of Thelephora, Stereum, Polyporus 



