Hollowat. — Prothallus, &c, of Tmesipteris. 



409 



angle to the primary shoot, being sometimes almost in a straight line with 

 it (figs. 73, 76, 78, 81, 83). Comparison may be made with those illustrated 

 in my other paper in figs. 68, 69, and 71. I have not observed the 

 actual initiation of this secondary apex when thus late developed, but 

 fig. 60 represents an early stage. It is, of course, adventitious in origin, 

 and, judging from what takes place in the case of the origin of lateral 

 adventitious shoots on both old and young rhizomes, an apical cell is cut 

 out from one of the surface cells while at the same time the inner cells 

 lying between this and the vascular strand of the primary shoot divide 

 longitudinally to form conducting-elements. I have observed a few 

 instances out of the large number of plantlets examined in which the 



Fig. 64.- — -The point of attachment of the young prothallial plantlet shown in 

 Plate LXIJI, fig. 3, in longitudinal section, showing foot, basal 

 wall, and accumulation of starch. X 100. 



secondary apex was not situated at the base of the primary stem, 

 but much higher up. One such plantlet is shown in fig. 61 in longi- 

 tudinal section. In this the appearance is rather as if there had been a 

 dichotomy of the apex. However, I have never come across an undoubted 

 instance of such dichotomy in a young rhizome, although it may be seen 

 in older rhizomes. Plantlets in which two primary apices of growth are 

 present are shown in longitudinal section in figs. 62, and 63, and in general 

 view in Plate LXIII, fig. 3, and in figs. 75 and 83. A corresponding 

 instance was given in my previous paper (fig. 70). Fig. 64 is a longi- 

 tudinal section of the point of attachment of the young plant shown 

 in Plate LXIII, fig. 3. 



