IRRITABLE RESPONSE 227 



Demonstration Methods. The influence of gravitation in deter- 

 mining the direction of growth of young parts may most effectively be 

 shown by growing similar seeds under conditions precisely alike except 

 that one set is kept revolving in a vertical plane, while the other keeps an 

 upright position. This may be accomplished simply and very effectively 

 by the arrangement figured herewith (Fig. 64), which may be constructed 

 from wood in the laboratory, and will later be supplied in efficient form 

 among my normal apparatus. It consists of a wooden frame revolving in a 

 darkened moist-chamber on the supported end of a Klinostat rod and dip- 

 ping its bars under water at each turn. One of the bars is fixed to the frame, 

 but the other is freely movable on pivots, and, moreover, has a weight which 

 keeps it always in one position relative to gravitation. If, now, sets of 

 seeds are pinned in corresponding positions to the two bars (half on one 

 side and half on the other for better balancing), and the Klinostat is set in 

 motion, the two sets are under precisely similar conditions, even to being 

 watered alike, except that one set is always in the same position as to gravi- 

 tation, while the other is constantly changing. In fact this method leaves 

 little to be desired in its effectiveness of demonstration of this subject. 

 Methods of demonstrating geotropic and other movements to audiences by 

 projection are described by Pfeffer in a paper earlier cited (page 23). 



The foregoing experiments are concerned with the determin- 

 ants of the positions of the main root and main stem, leaving it 

 still to be ascertained : 



Is gravitation concerned in determining the positions oj side 

 roots and steins? 



Experiment. In a moist-chamber of the germination-box, or 

 glass-and-paper, type, germinate seeds of a kind in which the young 

 seedlings early develop side roots (e.g., Bush Bean, Radish), and, as 

 soon as the side roots are from 1 to 2 cm. long, swing the glass plate 

 in the same plane through 45°, and observe the results. Later restore 

 it to the old position. (It will also be of interest to revolve the plants 

 on the Klinostat in the plane of the glass.) 



Experiment. Select a potted plant having slender growing side 

 branches, and, tying the main stem to a rod thrust into the earth, 

 tip pot and rod to 45° from the vertical, and observe the position of 

 further growth of the side branches. 



These studies will suggest a further inquiry as to whether 

 other parts of the plant, leaves, flowers, tendrils, etc., are geotropic, 

 matters which the student may in part settle for himself by aid 

 of the following: 



Suggested Experiments. Select a plant with slender-growing petioles 

 (e.g., Garden Nasturtium); tie its main stem to a glass rod; place pot 



