96 Dr. K W. Gamble and Mr. E. Keeble. [Apr. 24,. 



b. Thermotropism, Convoluta is attuned to a high heat-intensity. It 

 is athermotropic at ordinary temperatures. Just below the lethal 

 point (38 C.) it is negatively therraotropic. The response, however,, 

 is singularly and often fatally imperfect. 



c. Phototropism. Convoluta is positively phototropic, but only under- 

 certain conditions. A sudden elevation of light-intensity induces a 

 negative phototropism. Back-ground may inhibit phototropic response. 



At the moment of hatching Convoluta is aphototropic. The power 

 of response to light develops rapidly, appearing a few hours after 

 hatching. 



The anterior end only of animals divided transversely is photo- 

 tropic. 



The rays active in producing phototropism are the green. The blue 

 rays, which are active in inducing movement in zoospores, in Euglena 

 and in plants generally (Pieffer 11 ), produce no tropic effect in Convoluta. 

 The red rays produce a feeble negative tropism. 



The tonic influence of light is more important than the tropic 

 influence. To the former influence is due the remarkable periodic 

 " tidal " movement which, as we have found, Convoluta performs. 

 After a spell of insolation, colonies sink below the surface, and after 

 a certain sojourn in darkness they return to the surface. These 

 movements synchronise with the covering and uncovering of the 

 Convoluta zone by the tides. They take place in colonies brought 

 into the laboratory, but do not occur when such colonies are kept in 

 darkness. Convoluta, after a certain spell of illumination, passes into 

 a condition of light-rigor. In this condition it is singularly inert and 

 susceptible to mechanical injury. 



d. Rheotropism. Convoluta reacts to changes in rate of flow of 

 water. In a moderate stream, it tends to move up stream. Under 

 the stimulus of a suddenly increased flow it sticks to the ground ; . 

 when this is impossible, it contracts itself and is carried down stream. 



IV. Ecology. 



A. Previous Observations. Geddes and Von Graff have recorded the 

 distribution of Convoluta along the shores of the He de Batz, lioscoff. 

 They describe the rapid disappearance of the colonies when the sand 

 is tapped or when the tide flows over them. They suggest that 

 light and gravity provide the stimuli whereby these movements are 

 regulated. 



B. Observations of the Author*. The Convoluta zone is determined by 

 the outflow of drainage tidal water. The upper limit of the zone 

 corresponds to the high- water mark of lowest neap tides. This 

 situation insures the maximum of light-exposure consistent with 

 security from desiccation. Convoluta is neither a sub-aerial nor a 



