JACQUES LOEB 709 



part of the stem is now left, while the basal roots have developed* 

 Only at the base of the apical shoots roots may continue to grow. 



The suppression of the growth of the more apical roots at the 

 time when the roots at the base of the stem begin to grow is the ana- 

 logue of the suppression of roots in a leaf the apex of which dips into 

 water, as in Figs. 13 and 14. 



These ideas raised the question whether it would be possible to 

 suppress the roots at the base of a stem by putting the apical roots 

 into water, thereby accelerating their growth. Fig. 20 shows such 

 an experiment. Short pieces of stems with a pair of leaves at their 

 base and one node in front were dipped with their apices into water. 

 The root and shoot buds of the apical nodes were removed and only 

 one stem (the lower one in the drawing) formed roots at the apex 

 which grew rapidly. The air roots at the base of this stem which 

 had begun to form dried out and never grew again while the air 

 roots at the base of the three other stems (which had formed no 

 roots at the apex) continued to grow. The drawing was made on 

 the 26th day of the experiment. It is, however, not very easy to 

 cause abundant root formation at the apex and hence this experi- 

 ment will have to be repeated. 



VI. The Role of Nodes in Root Formation. 



The reader will have noticed that in order to demonstrate that 

 roots can be formed also in the apical regions of a piece of stem we 

 used isolated pieces of a stem with two leaves at the basal end. 

 The basal leaves must be large since the mass of new roots formed 

 increases with the mass of the leaf. If the leaves are not at the 

 base but in the middle of the leaf, or, more correctly, if the piece 

 of stem basally from the leaf includes one or more nodes, the root 

 formation in the stem apically from the leaf is generally suppressed. 

 The nodes basally from the leaf act like basal roots in preventing 

 root formation in the more apical region. This has been verified in 

 different ways some of which may be described. 



When we select long stems with one large leaf at the base of the 

 stem, and suspend them horizontally in moist air, roots develop first 

 at some of the nodes apically from the leaf, and later in abundance 

 at the base of the stem near the cut end (Fig. 21). Though these 



