REGENERATION IN PLANTS 73 



tions, but suspended with the basal end uppermost, results that are 

 in many respects similar to the last are obtained. Roots appear 

 around the base of the piece, i.e. around the upper end, and the leaf- 

 buds that develop are those that stand nearest to the apical, at present 

 the lower, end of the piece. 



These results seem to indicate that, in the main, the chief factors 

 that determine the growth of the new part are internal ones ; and 

 although internal factors do appear to be the dominating ones, since 

 roots appear in both cases at the base and shoots at the apex, yet it 

 would be wrong to conclude that gravity has no influence at all on the 

 result. In fact, other experiments show that it does have an influence. 



If an older branch (8-12 mm. in diameter) is cut off and hung up 

 with its base upward, the result is somewhat different from that with 

 younger branches. The roots appear along the entire length of the 

 piece, as shown in Fig. 32, B; the largest are those near the base, 

 and they decrease in size toward the apex of the piece. It is also 

 noticeable that all the roots come from preexisting root-buds, and no 

 adventitious roots are formed, even at the base. The leaf-buds that 

 develop are those arising near the apex, as in the last experiments. 

 They bend upward as they grow longer. A comparison of the 

 results obtained from younger and older pieces may, at first, seem 

 to show that the difference in their development is due to the greater 

 amount of reserve food stuff in the older piece, and Vochting thinks 

 it probable that this influence may account for the strength, length, 

 and even for the number of roots that develop, but he believes that it 

 is improbable that their mode of origin and their location can be so 

 determined. Furthermore, the development of new roots around 

 the base of the younger piece can hardly be explained as due to the 

 absence of food stuff. The explanation of the production of a smaller 

 number of roots in a young piece is that its tissues are less highly 

 specialized, its buds less advanced, and the piece itself is in a lower 

 stage of development. Another explanation must be found for the 

 greater number of roots that develop in the older piece. This is due, 

 as Vochting tries to show, in part to the influence of gravity on the 

 piece. 



Vochting's general conclusion is that " the force or forces that 

 determine the polar differences in the piece are most evident and most 

 energetic in very young twigs ; that this difference decreases with the 

 age of the twig whose leaf-buds and root-buds become further devel- 

 oped. It is clear that the new roots of young twigs could appear in 

 corresponding number and strength in exactly the same regions in 

 which they grow out from pre-formed buds of a year-old twig. Since 

 this does not occur, and since the roots appear only near the base of 

 young twigs r the explanation must be that the innate polar forces 



