MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 307 



ness, and to such an extent that shoots are formed which may exceed 

 the normal both in length and diameter. 



It is obvious that, in the above phenomena, the effects are due to 

 the stimulating influence of light, and of darkness (or absence of 

 light). The differentiation of the tissues, and the development of 

 certain reproductive bodies constitute positive reactions to the stimu- 

 lating influence of the rays, and the exaggerated elongations shown 

 by many shoots is a response to darkness, which may be adapta- 

 tional in its character, and which might serve to lift the chlorophyl- 

 bearing organs past an imaginary obstruction into illumination. The 

 failure of a large proportion of the forms examined to make an accel- 

 erated or exaggerated growth when freed from the influence of light, 

 even when provided with an adequate food supply, shows that light 

 has no invariable and universal relation to increase in length, or 

 thickness, or to the multiplication or increase in volume of the sep- 

 arate cells. 



When a green plant is suddenly deprived of illumination a marked 

 acceleration of the rate of elongation ensues, and a diminution ensues 

 when a plant is brought from darkness into light, which Pfeffer, as a 

 result of a consideration of the investigations upon this point, esti- 

 mates to amount to changes in the rate not greater than fift}'- per cent, 

 of the existing rate. Many of the observations bearing upon this 

 point were made with plants which do not exhibit an abnormal elon- 

 gation in darkness. In my own investigations the peduncles and 

 scapes of Arz'saema, which had ceased to make an amount of growth 

 equal to a total of i mm. per day, underwent a comparatively enor- 

 mous acceleration which reached a maximum about twenty-four 

 hours after being deprived of illumination, and then decreased to a 

 minimum correspondent to the original rate in about a hundred hours. 

 Arisaevia is a plant which shows a marked adaptational elongation 

 in darkness during etiolation, and this increase may only be ascribed 

 to the stimulative action of darkness, since it would be an obvious ab- 

 surdity to ascribe such an enormous increase in rate to the absence 

 of any direct or paratonic action of light. This seems still more 

 justifiable when it is pointed out that the rate of growth is never di- 

 minished by the action of light to the extent that it is by temperature. 



It is clear therefore, that no evidence is afforded by the behavior 

 of plants in darkness to support the conclusion that light directly 

 affects the rate of growth, since not all species exhibit increased 



