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GEO-PRESENTATION 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 

 heliotropically 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 



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



^ ing curvature. 



00 69] [Botanical Gazette, vol. 70 



