706 



PHYSIOLOGICAL BASIS OF POLARITY. II 



existence and activity of these root buds. The simplest method 

 of doing this is represented in Fig. 17. Vigorous stems con- 

 sisting of five or six nodes are deprived of all leaves except those at 

 the base. These basal leaves should be large since, as we have seen, 

 the mass of root formation increases ceteris paribus with the mass of 

 the leaves. The stems are suspended vertically in moist air so that 

 the basal cut end just dips into water. In about 3 or 4 days (at 

 . greenhouse temperature and with good illumination) shoots and roots 

 begin to grow out simultaneously. Fig. 17 gives a picture of such an 



Fig. 17. Stems with two large leaves at base, the latter dipping in water, 

 showing that roots form in many of the nodes situated apically from the leaf 

 from buds situated above the shoot bud. Drawn after 6 days. 



experiment after 6 days. The shoots are represented in thick black 

 spots and the roots in double lines, thus imitating their natural ap- 

 pearance since the buds are at first dark red and the roots are, of 

 course, white. It is obvious that each root takes its origin above 

 (apically from) the bud. 



About a week or 8 days after the preformed root buds have 

 grown out from the stem, the formation of roots at the base near the 

 cut end begins (Fig. 18), Under the conditions of our experiment 

 they touched the water and began to grow very rapidly. As soon as 



