METHODS 7 



ments cut off from two of its surfaces. Sections through young shoots 

 whose apices are just turning upward, showed in one case five apical 

 cells, of which it was impossible to say which was the original one. Some 

 of the initial cells had not yet divided, while in others one or more seg- 

 ments had been cut off. The original apex continues its growth upward, 

 while these secondary initial cells are left behind, but later they may give 

 rise to ventral shoots. 



Fig. i. 



A. Male plant of Pallavicima (Mittenia) Zollingeri. x 2. 



B. Sterile plant of P. radiculosa, natural size ; r, ventral branch. 



One of these secondary apical cells begins active growth and gives 

 rise to the shoot which continues the sympodium. It grows horizontally 

 for a time, but finally turns upward and develops into the next upright 

 green frond. Several segments are cut off from the apical cell before 

 a differentiation of the different tissues of the shoot is apparent. Finally 

 the midrib and lateral wings can be distinguished, and in the former the 

 central strand of elongated cells appears. Thus, at the base of the shoot, 



