THE DIFFERENTIATED PLANT 191 



course if a Wortmann or other large clinostat is available, 

 plants of any size may be used ; but if only the small clino- 

 stat made from a clock, as recommended for geotropism ex- 

 periments (page 184), is at hand, then a very light flower-pot, 

 preferably not over three inches in diameter, is needed, and 

 seedlings growing in Sphagnum moss may be used. 



Numerous supplementary experiments may be tried, such 

 as allowing the parts to become turned to light, and then 

 exactly reversing them by turning the pot through 180. 

 Indeed, this simple experiment is almost as satisfactory as the 

 clinostat. Again, the negative heliotropism of roots may very 

 easily be illustrated by the familiar experiment given in most 

 books (as in MacDougal's Physiology, page 59, Fig. 54). 



Observation of their experiments and of other cases should 

 lead students to see for themselves that stems turn into the line 

 of the light, while leaves turn at right angles to it, and they 

 can easily be led to see the meaning of this : the light being 

 necessary to the leaves, they expose their flat surfaces to it, 

 while the stems take that direction to help expose the surfaces 

 of the leaves. The very close analogy of the process with 

 geotropism should be emphasized. 



VI. The Differentiated Higher Plant 



23. Study the Bean plant, a well-differentiated plant. 



Observe every constant external feature, and 

 properly record. 



Finally, remove it from the pot, wash away the 

 soil, and observe the structure of the roots. 



24. In comparison with the Bean, observe fully the 



Coleus and the Balsam (Impatiens). (It is not 



