210 



AGRICULTURE. 



of the Petri dish and hold it hi position by means of 

 clips made of spring brass wire (Figs. 51, 52). (See 

 Stevens' " Botany," p. 25.) Wind the clock, and set it in 

 its normal position that is, with the hour-hand spindle 



"Introduction to BoUny." Copyright, 1M)S, by D. Heath * 



FIGS. 51 AND 52. SEEDLINGS OF INDIAN CORN 



Grown in sawdust in a Petri dish 

 while revolving by clockwork one 

 revolution per hour. The axis of 

 revolution is horizontal, the plane of 

 the dish vertical. Gravity as a direct- 

 ive agent is eliminated, and roots and 

 shoots grow out in the direction in 

 which they happen to be pointed. 



Grown in sawdust in a Petri dish 

 which was kept stationary in a ver- 

 tical position. Gravity is acting as a 

 directive agent, and the roots find and 

 take the downward and the shoots 

 the upward direction, irrespective of 

 the directions toward which they 

 were originally pointing. 



horizontal. Prepare seeds in another dish in exactly 

 the same manner, but fasten it so that it will stand ver- 

 tically on its edge. 



In the first experiment the directive effect of gravity 

 would be neutralized by the revolution of the dish, 

 while in the second gravity may exercise its usual influ- 

 ence on the direction taken by root and shoot. Compare 

 results as to direction of radicle and plumule.* 



* Since the seeds are not covered by the sawdust, their progress 

 in germination may be observed at any time without interrupting 

 the experiment. The position occupied by the parts of the seed- 

 lings can easily be recorded for any period by tracing with ink 

 on the cover immediately over them. 



