126 THE MORPHOLOGY OF PTERIDOPHYTES 



Carboniferous) had a shallow gutter-shaped stele with three 

 protoxylems (Fig. i8F), whereas B.forensis (Permian) had a 

 stele shaped like the Greek letter oj in transverse section, with 

 up to fifteen protoxylems (Fig. i8G). Some of these later 

 species, furthermore, are known to have had laminate 

 pinnules (Fig. i8I). 



The complexity of the branching of the later species of 

 Botryopteris is illustrated by the reconstruction of the stelar 

 system ofB. trisecta (Fig. i8H). Its erect stem had a cyhndri- 

 cal protostele and bore leaves in a spiral sequence. The 

 petioles had an oval vascular strand and branched into three. 

 The two lateral branches then trisected again but, whereas 

 the median traces in each case were co shaped, the lateral 

 ones were cylindrical, Uke the stem stele. The whole frond 

 was arranged in three dimensions, except for the ultimate 

 pinnules which were disposed in one plane. 



Associated with this plant were found some remarkable 

 spherical masses, containing thousands of sporangia, which 

 are believed to represent the fertile parts of the frond, al- 

 though in the meantime they are described under a separate 

 specific name, Botryopteris globosa. The whole mass was up 

 to 5 cm across and had, running through it, a system of 

 branches with w shaped steles, but how it was connected to 

 the parent plant is not known. Each sporangium was pear- 

 shaped (Fig. 1 8 J) and the distal half consisted entirely of 

 thick- walled cells, except for a stomium of thin-walled cells 

 over the apex. In most species of Botryopteris, the sporan- 

 gium wall is described as only one cell thick, suggesting that, 

 in this respect at least, they were leptosporangiate. It is 

 apparently true of some of the sporangia of B. globosa, but 

 not of all, for some clearly had a second layer of thin-walled 

 cells on the inside. This may well have shrivelled after the 

 spores had been shed, so becoming invisible when petrified. 

 Thus, although approaching the leptosporangiate condition, 

 B. globosa had certainly not yet achieved it, and the same is 

 probably true of all the species. 



