212 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



A modification of the normal conditions by which the customary 

 nocturnal period of darkness is lengthened to extend completely over 

 the vegetative period, and to include the entire possible development 

 of the plant exercises much more marked and quite sweeping effects. 

 In the first place all of the direct influence of light is lacking, and in 

 the analysis of the results of such etiolations it is necessary to take 

 into account most rigidly the general relations of every species to light, 

 as well its mode of life, seasonal habit, and mode of nutrition with 

 respect to the accumulation and use of reserve food material. 



The growth of a plant in darkness deprives it of the determinative 

 and morphogenic influence of light in all of the various phases, and 

 causes it to assume a stature wholly determined by its autotropic and 

 geotropic reflexes and their correlations entirely uninfluenced by pho- 

 totropic, or photolytic reactions. It is equally undeniable that etio- 

 lation must create most serious disturbances in the nutritive system. 

 The photosynthetic power usually exhibited by chlorophyllaceous 

 organs is wholly lacking, and if the plant is autotropic in its method 

 of subsistence it must prosecute its entire development by the aid of 

 reserve food laid up in its storage tissues. The amount of this ma- 

 terial, even in seedlings, is usually far in excess of that needed for 

 the stage of development for which it is provided, but when the plant 

 is forced to depend upon this supply by confinement in the dark room, 

 for the construction of organs and tissues usually supplied from the 

 foliar organs, variations may be expected. These variations may 

 consist in partial atrophy, or non-development of the organs con- 

 cerned, and of alterations in the differentiation of the tracts conduc- 

 ting plastic material to and from the affected organs. The etiolative 

 condition implies the establishment and maintenance of currents of 

 plastic material by no means identical in volume, character, direction 

 and location with those of the normal plant. Lastly, the relations 

 of the body to water are most profoundly modified. The decrease 

 in the formation of stomata, or the total failure of differentiation of 

 these organs lessens the power of transpiration of the plant, and is 

 followed of course by a much diminished movement of water and fluids 

 in the body which must materially affect all translocation processes. 



In addition to these negative effects of continued confinement in 

 darkness the probability is near that darkness exerts a direct effect 

 ■per sc upon the plant, an aspect of the subject which will receive 

 some consideration in the following pages. 



