CHAPTER VI. 



GROWTH AND MOVEMENT. 



PROVIDING MATERIALS. 



For most of the following observations, plants growing under natural 

 conditions out of doors are to be employed. Only those plants should 

 be selected which are thrifty and in a growing condition. In obtaining 

 root tips of onion, place the bulbs on moist carpet or blotting paper, 

 and cover with a bell jar. When the roots have grown out about T 3 6 of 

 an inch, cut them off with a sharp knife and place them in a i % solu- 

 tion of chromic acid in water for 48 hours ; then wash in running water 

 for half a day, and place in 20 % alcohol for a few hours, and for the 

 same length of time in 50 % alcohol, and finally in 70 % alcohol. After 

 being prepared in this way the roots may be kept indefinitely in equal 

 parts of alcohol, glycerine, and water. 



Good sections for our present purpose can be obtained by embedding 

 the roots in elder pith, and making longitudinal sections free-hand with 

 a sharp razor (see page 377). Thin median sections should be stained 

 in a solution of Safranin (see page 388), and mounted for examination 

 in dilute glycerine. There are more elaborate methods for preparing 

 uniformly thin sections by embedding the material in paraffin, and cutting 

 the sections with a microtome (see pages 383 and 386), but these methods 

 are not necessary for this study, since a few good sections may serve for 

 demonstration to the entire class. 



In selecting stamen hairs of Tradescantia, only those should be chosen 

 whose cell sap is still colorless. These hairs of different ages might be 

 used in place of sections from the onion root tip, but they are not so 

 satisfactory as well-prepared sections. 



It is a simple matter to grow seedlings of the sensitive plant, Mimosa 

 pudica, in pots under bell jars. The soil should be a mixture of equal 

 parts of rich garden soil, sifted sand, and well-rotted manure. The pots 

 should be kept in a warm place, and as soon as the seedlings appear, 

 the bell jars should be raised at one side. The pots should be kept 

 well watered. 



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