MEMOIRS OF THE NEW YORK BOTANICAL GARDEN. 



193 



trol chamber in full illumination until the plumule 

 of the young shoot was almost disengaged from be- 

 tween the cotyledons, and the curved portion of the 

 stem already exposed bore a pair of small quinate 

 leaves. The plantlet was then removed to the dark 

 room and allowed to continue growth. Not only did 

 the leaflets of the first pair of foliar organs continue 

 growth, attaining nearly double the size shown at the 

 time of their removal to the dark room, but all of the 

 leaves borne on the etiolated and erect stem a month 

 later also had five small leaflets which were en- 

 tirely lacking from perfectly etiolated seedlings. It 

 is thus to be seen that the stimulation of light upon 

 the basal portion of the young shoot induced the de- 

 velopment of laminar members on internodes which 

 not only were not exposed directly to the light, but 

 which were not developed until some time later. The 

 evidence afforded by this demonstration also bears 

 most strongly against the acceptance of any etiolation 

 results in which light is excluded from a portion of 

 the plant only. 



Small trees of this species were cultivated by Bon- 

 nier in a continuous illumination from electric arcs of 

 such intensity that oxygen was given off at one-third 

 the normal rate by aquatic plants. Under such condi- 

 tions the shoots did not attain normal size and elon- 

 gated more slowly than under the usual conditions of 

 alternating daylight and darkness. True foliar leaves 

 were produced which were very green. No differen- 

 tiation of bark or lenticels ensued, and the cortex was 

 thinner than in the normal, as well as the central 

 cylinder. The cortex was differentiated into two 

 zones as it appeared to do under both normal condi- 

 tions and in absolute darkness, in the experiments de- 

 scribed above. The sinuosities of the pericycle were 

 less accentuated. The thickening of the pericycle was 

 less marked, and the woody tissue was less perfectly 



Fig. 150. AEsculus Hippocastanum. EtiolatedJ seedling 60 

 dajs old. 



N- 



