3 i6 



STUDIES IN FOSSIL BOTANY 



remembered, however, that in these Botryopterideae we 

 are often dealing with specialised fertile fronds. 



Our illustration (Fig. 1 1 8) is taken from the petiole 

 of another species, Z. bibractensis ; Ren., in which 

 the structure is rather more complex. The bundle 

 has essentially the usual H-like sectional form, but 



hy ic 



x 



-^» ' -yi N 



Fn„ no. — Zygopteris bibractt.>isis. Transverse section of a petiole, showing the double- 

 anchor form of stele, .r, middle band of xylem ; x' . the main lateral bands ; x", the 

 small-celled external arcs of xylem ; the protoxylem lies between x' and x" ; i.e., inner 

 cortex ; hy. sderenchymatons hypoderma. X 7. From a photograph by Mr. L. A. 

 Boodle. S. Coll. 014. 



the lateral pieces are considerably incurved, giving 

 to the whole the shape of a double anchor. The 

 peculiar feature of this species consists in the presence 

 of an additional external band of xylem (x) on the 

 outer side of each of the lateral plates (V), separated 

 by parenchyma from the main lateral plate, but united 

 with it at its two ends (Fig. I I 8). The external bands 



