126 REGENERATION 



tissue spaces, that is the gaps between the cells or the tissues. As 

 had been stated previously, it is chiefly the tissue sap flowing in 

 these latter channels which is influenced by gravity collecting on 

 the lower side of a stem or a leaf; while the sap flowing in the 

 regular vessels is less or not at all influenced by gravity. The 

 vessels for the descending sap from an apical leaf lie on the side 

 where the leaf is attached. When we remember that the descend- 

 ing sap from a leaf inhibits shoot formation in its path we can 

 understand the results in Figs. 100 and 101. 



In Fig. 101 the tissue sap will go to the lower side of the stem 

 and on this side flows also the descending sap from the leaf 

 following the regular vessels, since the leaf is on the lower side of 

 the stem. Hence we have no shoot formation on the lower side 

 of the two stems in Fig. 101, but we notice root formation on the 

 lower side and in both cases in the second node and in the fourth 

 node basally from the leaf. These are the nodes in which the 

 inhibition of shoot formation is most complete. Old stems with 

 one apical leaf suspended vertically can form shoots in the first 

 node below the leaf; in the second node only on the side of the 

 stem opposite the leaf, but not on the side where the leaf is 

 attached. The anlagen for shoots in the second and fourth 

 nodes, on that side where the apical leaf is, lie in the middle of the 

 path of the sap flow descending from the leaf and here the inhibi- 

 tion of shoot formation is most pronounced. As Fig. 101 shows, 

 in the second and fourth nodes basally from the leaf and in the 

 same node as the leaf the formation of roots is most favored. 

 It is natural to correlate these two facts. 



The question then remains why shoots can arise more easily in 

 the first node basally from the leaf when the leaf is on the lower 

 side of a stem placed horizontally than when the stem is sus- 

 pended upright and vertically. This is intelligible with the aid 

 of Fig. 70 (Chapter XII) which shows the path of the sap descend- 

 ing from a leaf. The two anlagen for shoots in the first node 

 basally from the leaf lie at the outer edge of the sap flow from the 

 apical leaf. When the stem is suspended vertically and upright 

 the two anlagen for shoots in the first node below the leaf will be 

 bathed in tissue sap escaping from the vessels containing the 

 descending current from the apical leaf. When the stem is 

 placed horizontally some of this sap will sink, thus allowing 

 some of the buds in the first node below the leaf to escape the 

 full consequence of inhibitory effect. 



