428 



ME. F. DARWIN ON THE POSITION OF 



Lateral position. — The position shown in fig. 5, in which the 

 spindle of the kliuostat is still parallel to the incident light, but 

 the axis of the plant is perpendicular to the axis of rotation, is 

 equivalent to a strictly lateral illumination if the plant were not 

 on the klinostat, and is called the " lateral position." 



Diagram illustrating the "lateral position." 

 kJc, spindle of klinostat ; B, box; A, hypocotyl ; x, y, cotyledons; the arrows 

 give the direction of incident light. 



The other possible positions are when the axis of the plant is 

 either parallel or perpendicular to the axis of rotation, and the 

 axis of rotation is perpendicular to the incident ligbt. These are 

 the positions in which, as Sachs has shown, geotropic and helio- 

 tropic curvatures are both excluded. 



Fig. 6. 



Diagram illustrative of the terms " transverse plane " &c. 

 k k, B, h, as in fig. 5 ; 1 1, the transverse plane ; a, b, cotyledons making an 

 angle <t> behind the plane 1 1 ; .r, y, cotyledons making an angle 9 in f r0}it 

 ottt. 



Transverse plane is the plane at right angles to the axis of 

 the plant. In fig. 6, if h is the hypocotyl of a seedling plant, 1 1 is 

 the transverse plane. If the cotyledons are bent back towards 

 the stem of the plant as shown at a and b, then they are said to 

 be behind the transverse plane. The cotyledons x and y are in 

 front of the transverse plane. All angles in front of the trans- 



