Growth 341 



to require being set free. It is not at all evident why 

 wilting may be favorable to many cuttings, unless, perhaps, 

 there is a tendency to permit too many leaves to remain 

 on the cuttings, the vigorous activity of which is then 

 permanently checked or inhibited by the wilting. 



201. Growth movements. Growth movements of 

 the varied sorts known may be referred to two types. 

 These are (1) autonomic, or those resulting from internal 

 and generally unknown conditions, and (2) paratonic, 

 resulting as a response to external conditions or stimuli. 

 Such movements are discussed in the special chapter on 

 growth movements, also in those chapters dealing with the 

 relations of plants to single environmental factors. It is 

 sufficient here to note that there are various types of 

 growth movement. 



LABORATORY WORK 



Elongation of root and shoot. Determine the growing region 

 of roots of the horse bean, bean, or field pea. Use germinating 

 seed in which the radicle has developed to the extent of from 1 to 

 \\ inches. With a fine thread dipped in India ink mark off parallel 

 lines at equidistant intervals, of from 1 to 2 mm., placing the 

 first mark in one or two cases as near the root-tip as possible and 

 in other specimens at a full interval from the tip. Make daily 

 observations and measurements and give a table or plot curve 

 of the results. In order that the marked seedlings may be kept 

 under suitable conditions, place each in the bell of a thistle tube 

 (containing a little moist moss) with the root extending into the 

 tube, the lower end of the latter resting in water. Favorable 

 conditions may also be secured by pinning the seed, with the 

 roots projecting vertically, to the bottom of a large cork to which 

 has also been fastened moist filter or blotting paper. The cork 

 is then fitted into a tumbler containing some water. 



