CALAMOSTACHYS 



55 



the fourfold division, so general in spore mother-cells, 

 already prevailed among these Palaeozoic plants. In 

 many cases the spores of the same tetrad are very 

 unequally developed, some remaining quite small 

 (Fig. 22, B and C) ; we may regard the latter as 

 abortive spores, their suppression having allowed of the 

 better nutrition of their surviving sister-cells. The mature 

 spores show a triradiate marking on one side, probably 



lmL_ 



Fig. 21. — Calamostachys Binneyana. Part of tangential section of cone, showing 

 portions of two whorls of bracts (br) with sporangiophores (sp) between. Around 

 each of the latter the four sporangia' (sm) are grouped, br, free tips of other bracts, 

 x about 25. S. Coll. 175. (G. T. G.) 



indicating the lines of junction with the sister-cells 

 (Fig. 22, D). 



Numerous specimens of C. Binneyana, which is a 

 fairly common fossil, have been examined, and no traces 

 of more than one kind of spore have been found. Except 

 for occasional abortion all the spores are uniform. There 

 is thus a strong presumption that this species was homo- 

 sporous. In another British species, however, Calamo- 

 stachys Casheana, heterospory, as Williamson discovered, 

 certainly occurred. In general organisation this cone is 



