

GE0-PRESENTAT10N AND GEO-REACTION 



CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 268 



Eva O. Schley 



(with five figures) 



Historical 



The reaction of plants to geotropic stimulation has been the 

 subject of considerable investigation, the problem having been 

 attacked from many standpoints. Naturally, perhaps, the physical 

 side was studied first, a number of workers having developed the 

 main features of gravity stimulus, presentation and reaction times, 

 perception, conduction and response, organs of perception, and 

 other related subjects. The chemical side of the field, involving 

 the change in metabolism of the stimulated organ, has received 

 much less attention. 



The first worker in this field seems to have been Kraus. As 

 early as 1870 he published (14) the first of a series of researches on 

 the chemical content of the growing plant, both in normal relations 

 and after subjection to various external stimuli. This research 

 included (1) the water content, (2) the acidity, (3) the sugar 

 content of the normally growing shoot, (4) the relation of each to 

 the growth maximum, and (5) steps in the change of the cell 

 content of the concave and convex side of the geotropically and 

 helio tropically responding organ. He determined that, in the 

 normally growing shoot, (1) the acidity decreases from the tip 

 downward, (2) the water increases relatively from the tip to the 

 downward limit of growth, and (3) the sugar increases from the 

 tip below the growth maximum and therefore is not a limiting 

 factor in growth. In the stimulated organ he found on the convex- 



becoming side (1) an increase of sugar production up to the time 

 of visible curvature and then a decrease, (2) a progressive decrease 

 in acidity during stimulation, free acid being entirely absent from 

 the responded organ, and (3) a progressive increase of water preced- 

 ing curvature. 



69] 



Botanical Gazette, vol. 70 



