290 MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



This is illustrated by the seedlings of AEsctihis in which a brief 

 illumination of the basal internode, which is the only one developed 

 in normal plants during the first season, set up a stimulus which was 

 communicated to other internodes formed weeks later and in conse- 

 quence of which laminar bodies arose, which were invariably lacking 

 from absolutely etiolated seedlings (see p. 191). Another phase of 

 this reaction is to be seen in " partial etiolations " in which the ter- 

 minal portion of a shoot is confined in a miniature dark chamber and 

 the basal portion is illumined in a normal manner. Few experiments 

 of this kind are faultless in providing absolute exclusion of light from 

 the confined organs, and normal conditions of atmospheric humidity, 

 although in some instances care has been taken to secure proper 

 temperatures. The most striking of such tests were made by Jost, 

 in which he found that etiolated leaves might attain dimensions ap- 

 proximating the normal when a portion of the shoot was exposed to 

 light, and also that when only a few of the buds of the beech were 

 exposed to the light, others in darkness, which remained quiescent 

 when the plant was wholly darkened, awoke as a result of the stim- 

 ulation transmitted to them. The effects of transmitted effects of 

 stimulation by light have been analyzed by Teodoresco, who com- 

 pared the structure of normal leaves and stems with similar organs 

 formed on plants subjected to " partial etiolation," and also by plac- 

 ing an active green plant in darkness after it had made a certain 

 amount of growth. The organs enclosed in darkness attached to 

 shoots a portion of which was exposed to illumination attained a 

 greater size and a more complete stage of differentiation than those 

 found on plants which were first allowed to make a certain amount 

 of growth under normal conditions and then completely enclosed in a 

 dark chamber. The results here speak most clearly of a stimulative 

 action. The long-continued stimulation received by the exposed por- 

 tions of the shoot in partial etiolations would naturally be transmitted 

 and produce more marked effects in the way of perfection of tissues 

 and development of size than when the entire plant was placed in the 

 dark room and only the after-effects of previous exposure would be 

 present. Partial etiolations of flowers by Beulaygue resulted in 

 similar differentiations of the tissues of these structures. 



The separate and distinct effects produced by the various regions 

 of the spectrum are not easily analyzed. Sachs claimed to have 

 proved that the ultra-violet rays were necessary for the formation of 



