7H5 



sufticient (o cause a slight acceleration of urowtli in the anterior 

 wall. Since the posterior side is .somewhat more strongly illuminated 

 than the anterior one, which only just reacts, the posterior side 

 therefore begins to react sooner: after 4 to 5 min. a very slight 

 curvature occurs, after about 7 uiin. the anterior wall also reacts, 

 the very slight curvature does not continue or n:\ay even disappear, 

 but a distinct acceleration of growth of the entire cell can be observed 

 and as this passes off, there again occurs also a very slight curvature, 

 since the rather more strongly illuminated posterior wall not only 

 begins to react earlier, but continues to r^act somewhat longer 

 than the anterior wall, which falls just within the reach of a growth 

 acceleration. The phototropic curvature is thus divided here into 



two and both parts remain very slight. If somewhat more light is 

 supplied, the reaction-times of the anterior and the posterior- wall 



