JACQUES LOEB 459 



IV. Regeneralioji of Roots. 



Two kinds of roots are formed in an isolated piece of stem, suspended 

 in moist air and dipping with the base in water, first, air roots in the 

 nodes, and later roots at the basal end of the stem regardless of the 

 node (Figs. 1,3, and 7), The air roots in the nodes grow out sooner 

 than the basal roots but as soon as the basal roots grow out the air 

 roots dry out and die. This has been discussed in a previous paper. 

 We are interested here only in the basal roots since they alone are 

 connected with the problem of polarity. The regeneration of the 

 basal roots differs from the formation of apical shoots in this, that the 

 apical shoots begin to grow out almost immediately after the defoliated 

 piece of stem is isolated, while there is a long latent period before the 

 basal roots make their appearance. For this reason quantitative 

 measurements correlating the mass of the basal root formation with 

 the mass of stem require probably a longer time than that in our ex- 

 periments. A glance at the drawings will, however, convince the 

 reader that the root formation commences sooner in the stems with 

 larger mass than in the stems with smaller mass, regardless of the 

 original position of the piece of stem in the plant. 



Thus in Fig. 6 the large middle piece (3) forms roots before either 

 of the 2 more basal pieces form roots, and Fig. 7 shows that the relative 

 mass of roots produced seems also to run parallel with the relative 

 mass of the piece. The same phenomenon is shown if we compare 

 Fig. 1 with Fig. 2, or Fig. 3 with Fig. 4. It is also obvious in Fig. 5, 

 so that we can say that the mass of roots produced by pieces of de- 

 foliated stem of Bryophyllum calycinum increases under equal con- 

 ditions with the mass of the stem. 



V. Influence of Light on Regeneration in a Defoliated Stem. 



8 long defoliated stems were suspended into an aquarium kept dark 

 by a double cover of black cardboard, and 8 equally long defoliated 

 stems were put at the same time into an aquarium exposed in the 

 usual way to daylight. The base of the stems dipped into water. 

 All conditions were equal except the illumination. After 23 days all 

 the stems exposed to light had formed large basal roots and large 

 shoots at the apex (Fig. 8). At the same time none of the stems 



