CH. yii] 



DIAGEOTROPISM, 



177 



When a seed of Gucwrbita omfera (vegetable marrow) 

 is allowed to germinate in normal conditions the well- 



FiG. 36. Exp. S20. 

 known peg or heel, shown in fig. 36, A, is developed on 

 the physically lower side of the radicle I But if the seeds 

 are kept in slow rotation on the klinostat until they 

 germinate, the peg is not developed laterally but like 

 a frill all round, as shown in fig. 36, B. 



(221) Diageotrcypism or transverse geotropism. 



A bean, in which the secondary roots are just beginning 

 to appear, is placed in damp sawdust in one of Sachs' 

 trough-like glass vessels (see exp. 191). It must be 

 placed close to the glass so that the behaviour of the 

 secondary roots can be seen from outside. The trough 

 is placed in the dark and the slightly oblique direction in 

 which the secondary roots grow must be noted.. If it 



' Pig. 36 A is from the Power of Movement in Plants, p. 102. 

 D. A. 12 



