?fIAP. IV. 



DICOTYLEDONS. 



245 



leaf 51 inches in length, produced by a young plant 2 feet high, 

 growing vigorously in a large pot, was directed at an angle ot 

 about 45° beneath the horizon. On June 18th the leaf descended 

 from 10 A.M. till 1135 a.m. (see Tig. 109); it then ascended 

 greatly till 6 p.m., this ascent being probably due to the light 



Fig. 109. 



'uf asTp.mja'? 



Dahlia I circnmnntation of leaf, traced from 10 A M. June 1 8th to 8.10 A.M. 

 20th, but with a break of 1 h. 40 m. on the morning of the 19th, as, 

 owing to the glass filament pointing too much to one side, the pot had 

 to be slightly moved ; therefore the relative position of the two tracings 

 is somewhat arbitrary. The figure here given is reduced to one-fifth of 

 the original scale. Apex of leaf 9 inches from the glass in the line 

 of its Inclination, and 4^ in a horizontal line. 



coming only from above. It zigzagged between 6 r.M. and 

 10.35 P.M., and ascended a little during the night. It Rhould be 

 remarked that the vertical distances in the lower part of the 

 diagram are much exaggerated, as the leaf was at first deflected 

 beneath the horizon, and after it had sunk downwards, the 

 filament pointed in a very oblique line towards the glass. Next 



