NOTES ON srH^KOCARPUS. 75 



divide rapidly so that before the first division takes place 

 the end of the germ-tube appears bright green; in the basal 

 part of the germ-tube chlorophyll is almost completely 

 absent. 



The first division wall arises near the end of the germ-tube 

 and separates most of the granular protoplasm from the col- 

 orless part of the tube. This first wall is followed in most 

 cases (Fig. 2), by one or two others parallel with it, before 

 any longitudinal divisions occur. The next divisions are 

 variable and it is difiicult to say what is the commonest 

 arrangement of the secondary walls. Sometimes by two inter- 

 secting longitudinal walls in each primary cell, except the 

 long basal cell which undergoes no further divisions, the 

 young plant assumes the form of a cylindrical body composed 

 of several tiers of four cells each; but more commonly the 

 divisions are less regular, one of the longitudinal walls being 

 suppressed in some or all of the primary cells, or the basal 

 cell may remain entirely undivided. 



If the first longitudinal wall in the terminal cell is ob- 

 lique, there is formed at once a two-sided apical cell (Fig. 3, 

 4) of the type found in Aneura and Metzgeria, and often in 

 the early stages of many other liverworts and the prothallia 

 of most ferns. Where four similar terminal cells are formed 

 by the intersection of two median longitudinal w^alls, one of 

 these usually becomes the single apical cell of the thallus, 

 and in most cases, by secondary divisions assumes for a time 

 the two-sided form. As soon as the apical cell is established) 

 the growth of the thallus is brought about by the formation 

 of regular segments cut off alternately right and left from the 

 apical cell. At this stage the thallus closely resembles that 

 of Aneura or a young fern-prothallium such as that of Os- 

 munda or Marattia, where from the first there is a thickened 

 central region. In a few cases observed, (Fig. 6) where the 

 fiirst longitudinal walls were strictly median, the formation 

 of a single apical cell was not so evident, the divisions on 

 both sides of the median wall being much alike. The apical 



