170 THE MYXOMYCETES OF P1CTOU COUNTY. MOORE. 



A series of careful experiments conducted by Rosanoft' (Mem. 

 de la soc. Imp. des. Sc. nat. de Cherbourg, T. XIV) on tihe 

 plasmodium of Fuligo ovata seems to establish that/ in this case 

 at least, the plasmodium is strongly negatively geotropic, the 

 general movement of the plasmodium on an inclined surface 

 invariably taking place against tihe force of gravity. The same 

 investigator observed a like tendency to progress against the 

 centrifugal force when the plasmodium was placed upon a 

 rotating plate. 



This negative geotropism is exhibited by many species in 

 connection with the fruiting phase, and appears to be an adap- 

 tion to provide for more effectual spore disposal. Preparatory 

 to fruiting, the plasmodic mass will ascend and often almost 

 completely envelop blades of grass, moss plants, etc., and these 

 points of vantage gained the transformation into nature spor- 

 angia takes place with astonishing rapidity. Particularly 

 noticeable for this tendency are the plasmodia of Physarum 

 wrescens and Pliysarum cinereum; but the characteristic is 

 exhibited in a greater or less degree by almost all species. 



Plasmodia also shew a marked sensitiveness to temperature 

 changes. That of Fuligo ovata is positively thermotropic up to 

 33 degrees C. 34 degrees C., but becomes negatively so above 

 tii at point. An exposure to a temperature of 2 degrees C. does 

 not kill this plasmodium, but all movement ceases and a pro- 

 longed exposure at that point eventually results in death. The 

 maximum temperature in the case of this species is 52 deg, C. - 

 53 deg. C. 



Intense illumination has also been found to check move- 

 ments of the plasmodium, and in unequal illumination it moves 

 towards the shade ; in varying moisture towards t<he more moist 

 side. The direction and rapidity of movement is also strongly 

 influenced by the presence of appropriate nourishment and, 

 moreover, the plasmodium shews a marked power of discrimina- 

 tion in this connection. A series of very interesting observations 



