Factors in Rrgrfirrafioti 353 



at the basal end only, while polyp formation at the lateral and oral 

 ends is largely inhibited. New stems and branches show a strongly 

 negative geotropism, and grow upward irrespective of the position 

 of the piece. 



2 Sunlight. Stems or branches exposed to the direct rays of 

 the sun regenerated a greater number of polyps than those kept 

 in the shade of the room, the temperature in both cases being 

 approximately the same. How much the increase was directly 

 due to the effect of the actinic rays per se, or indirectly to the 

 destruction of bacteria, or to the slightly increased temperature, or 

 to all of these factors was not ascertained. Many of the stems and 

 branches bend toward the sun, /. e., they are positively heliotropic. 



3 Tetnperature. Other conditions being favorable and equal, 

 regeneration increases with increased temperature to the optimum, 

 and decreases with the lowering of the temperature. At 10° C. 

 regeneration is largely inhibited, while regeneration increases up 

 to and including 28° C. temperature. One of the more important 

 conditions, just mentioned, is exposure to sunlight for stems placed 

 in water at a moderately high temperature and not exposed to 

 direct sunlight produces far fewer polyps. 



4 Any severe injury at any level of the colony, may cause polyps 

 to regenerate, if the wound be exposed to sea-water. The direction 

 of growth of the pedicels and the rate of development of the polyps 

 are subject to the external conditions mentioned and to the internal 

 conditions to follow. 



5 Contact, pressure, impact, etc., are inhibiting influences 

 which tend to prevent complete development at those ends that 

 come in contact or are pressed upon by a solid body. Shoots are 

 often produced, but further differentiation is stopped. Con- 

 tact determines, in some degree, particularly on very young 

 branches, the direction of growth, which is away from any solid 

 body, therefore, is negatively stereotropic. The amount of inhib- 

 ition is proportionate to the degree of contact, pressure, impact, etc. 



6 Large variations in the concentration of sea-water probably 

 never occurs in nature and the reactions of Eudendrium to differ- 

 ently concentrated solutions can hardly be called adaptive. The 

 maximum number of polyps regenerated does not occur in normal 



