CHEIROSTROBEAE 121 



cells, with their lateral membranes stiffened by buttresses, 

 precisely as in a Calamostachys. A similar structure 

 occurs, as we have seen, in Sphenophyllum Dawsoni. 

 The spores have an average diameter of .065 mm. ; 

 their outer membrane is ridged, the ridges apparently 

 corresponding to the lines of junction of the four sister- 

 cells. The specimens known are too few to afford 

 decisive evidence as to whether the plant was homo- 

 sporous or heterosporous ; it is worth noting, however, 

 that the sporangia at the base of the cone show no 

 difference from those borne near the apex, as regards 

 the dimensions of their spores. The peduncle much 

 resembles the axis of the cone itself, but in the 

 peduncle well-marked secondary tissues are present, 

 which in places are well preserved, so as to show the 

 phloem, and even remains of the cambium, as well as 

 the secondary wood, in which medullary rays can be 

 recognised, separating the rows of tracheae. In one 

 specimen of the cone slight secondary growth had also 

 taken place in the axis. 



The cone of Cheirostrobus pettycurensis is perhaps 

 the most complex Cryptogamic fructification at present 

 known to us, and it is a striking fact that it should occur 

 at so ancient an horizon as the base of the Carboniferous 

 formation. But, highly modified as it is, Cheirostrobus 

 bears the impress of great antiquity in the fact that it 

 is a synthetic type, combining the characters of very 

 different groups of plants. In its peltate sporangio- 

 phores, and in the insertion and details of structure 

 of its sporangia, Cheirostrobus agrees exactly with the 

 Calamarieae. In the anatomy of the stele, on the 

 other hand, it resembles a Lycopod, of the type of 



