50 JOSHUA ROSETT 



interposition of a horizontal obstacle in the course of the verti- 

 cally growing stem produces a branching of the stem on the 

 lower surface of the obstacle. These branches pass laterally in 

 all directions until at least one of them reaches the vertical side 

 of the obstacle, when it will continue upwards, while the rest 

 of the branches stop growing. If the tip of the stem is covered 

 with wax, or some other material so as to close up its opening, 

 it stops growing. In a few seconds, however, it is found that 

 a new stem grows either from the side of the old stem or from 

 the osmotic sac. If the tips of the branches are in their turn 

 closed up with wax, new branches shoot out either from the old 

 branches, from the main stem, or from the osmotic sac. In 

 this manner any number of branches can be produced at will. 

 When a branch grows from the side of the stem, the part of 

 the stem between the osmotic sac and the branch, thickens and 

 bends in a direction opposite to that where the branch arises 

 (see fig. 2, F). A breach in the weakest point of the stem wall,, 

 or sac, consequent upon the rise of pressure within the stem 

 and sac when t*he outlet is closed, explains the growth of branches 

 under these conditions. The pressure of the fluid within the 

 stem must rise when it is bent at sharp angles a number of times, 

 and this condition, too, accounts for the outgrowth of branches. 

 The same increase of pressure within the stem, forcing the per- 

 manganate solution through its wall, possibly accounts for the 

 thickening of the stem between the sac and the outgrowing 

 branch. The wall of the stem opposite to that from which 

 the branch grows, must be subjected continually to greater pres- 

 sure from within than that which bears the branch (the latter 

 having an outlet, the former having none — the principle of the 

 revolving garden-sprinkler), and this fact may account for the 

 bending of the stem between the sac and the branch in a direc- 

 tion opposite to that from which the branch grows. Thus it 

 apparently happens that the same factor which causes the out- 

 growth of a branch (the rise of osmotic pressure within) also, 

 enables the stem to withstand the increased weight occasioned 

 bj'' the new outgrowth. 



