8 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN 



anew, and his fortunate choice of material in the delicate spo- 

 rangiophores of Phycomyces, and the availability of apparatus for 

 temperature regulation, and of measurable sources of light made 

 it possible to secure data upon which some conclusions as to 

 beginning and following effects of illumination on growth, and 

 the influence of exposures of varying length and to a series of 

 intensities might be reached. Later, similar studies were made of 

 Helianthiis globosus. The behavior of the two plants included some 

 striking dissimilarities. The illumination of Phycomyces results in 

 an immediate acceleration, while in Helianthiis the primary effect 

 is a retardation. The course of growth in Phycomyces includes a 

 primary acceleration, then retardation with a final rising rate. 

 Helianthiis is first checked, then shows an acceleration, which 

 slackens gradually to the original course. 



Vogt^ has also made some measurements of the growth of the 

 coleoptile of Avena sativa, well controlled as to temperature and 

 light, in which it was found that the illumination of a plant (not 

 etiolated) is soon followed by an acceleration of growth, the 

 duration of which depends upon the intensity of the light. The 

 rate now falls off for a period, then rises to or above the normal. 



If these be taken in connection with my own findings of the 

 behavior of a plant deprived of illumination, viz: "In one series, 

 however, the peduncles and scapes of Arisaema nearing the end 

 of their period of elongation showed an initial acceleration when 

 light was totally excluded from the plants. This acceleration 

 reached its maximum in twenty-four hours then decreased to a 

 minimum equivalent to the original rate in about four times this 

 period," adequate ground will be found for the conclusion that 

 the reaction of plants in growth to light is due directly or indirectly 

 to physico-chemical changes effected by light-energy. 



Opportunity for reconsideration of the general problems of 

 growth developed at the Desert Laboratory two years ago and a 

 series of experimental observations was planned to make an 

 analysis of some of its phases. It was found that the various 

 instruments used in measuring growth, inclusive of several types 

 of auxanometers, balances, recorders, horizontal and traversing 

 microscopes are in their diversity both adequate and j^recise to 



' Vogt, E. Ubcr den Einfluss des Lichts auf das Wachstiim dcr Kulcoptile von 

 Avena saliva. Zcitsch. Bot. 7; 193-270. 1915. 



