3 oo STUDIES IN FOSSIL BOTANY 



going stele is very evident ; at F i , which is cut nearer 

 its exit, the trace is apparently divided into two, and 

 the sclerenchymatous zone has almost closed in behind 

 it. Stenzel found, however, that the two arms of the 

 leaf-trace always form part of a single horse-shoe or 

 elliptical bundle. 



A and B, at the sides of the figure, are the steles 

 from which the leaf-traces of the next pair of leaves 

 will be supplied, while D and E will give off, at a still 

 higher level, the traces for the pair lying above Fi and 

 F2. These four bands, corresponding in position to 

 the four orthostichies of leaves, may be called the 

 reparatory steles. At the four diagonal corners, we 

 see four very long and curved steles (P1-P4), the 

 " peripheral steles " of Zeiller, which have an important 

 part to play. For one thing, it is from them that the 

 adventitious roots take their rise ; such roots are shown 

 at several places between the peripheral steles and the 

 sclerenchyma, or just passing through the latter. The 

 peripheral steles are further concerned in the emission 

 of the leaf-traces, for they anastomose with the re- 

 paratory steles immediately below the point where the 

 leaf-trace passes out from the latter. Thus at C a 

 branch is seen springing from the peripheral stele P3 

 to join the reparatory stele B. 



The numerous internal steles — G, H, etc. — form 

 a cauline system, the members of which, however, 

 anastomose both among themselves and with the more 

 external steles. 



The whole subject of the vascular system of the 

 Psaronii has been worked out by Zeiller, Stenzel, and 

 Rudolf with a degree of completeness which could 



