120 



Prof. W. C. Williamson and Dr. D. H. Scott, [Feb. 



The sporangiophores are in verticils, placed midway between th< 

 of the bracts, and are usually about half as numerous in each whc 

 as the latter. 



The sporangiophores are peltate, resembling those of Equisett 

 each bears (four sporangia on its lower surface, attached near tl 

 edge. 



The structure of the axis of the strobilus has been studied 

 detail. 



The central cylinder, or stele (which may be either obt 

 triangular or quadrangular, as seen in transverse section), has 

 parenchymatous pith, of considerable relative size, around which 

 the collateral vascular bundles. 



In the triquetrous form their number is 3 or 6; in the 

 rangular type it is 4. The bundles are always placed at the pi 

 jecting corners of the stele. On the inner side of each bundle 

 gap, or irregular canal, in which the annular and spiral tracheae 

 the protoxylem are contained. 



The phloem is very rarely preserved, but in one specimen could 

 clearly recognised. 



The structure of the bundles, both in the internodes and node 

 is essentially similar to that of Calamites, the chief differences coi 

 sisting in their small number and less definite canals. 



In many of the axes a zone of secondary wood, of considerabl 

 thickness, was formed. 



Vascular bundles pass out into each bract and sporangiophore. 



In the latter the bundle forks twice, and each of the four branche 

 runs out, through the peltate expansion, to the base of a sporangiui 



The sporangial wall, as preserved, is usually a single layer of cell 

 which have their walls thickened in a manner resembling that of tl 

 " fibrous layer " of some anthers. 



The spores are all of one kind. No trace of macrospores 

 found in any of the numerous strobili of this species which we 

 examined. 



The spores attain a diameter of about 0'09 mm. In some sj 

 mens they are isolated ; in other sporangia they are still grouped 

 tetrads, each tetrad being enclosed within the wall of the raothe 

 cell. 



It is rare for all the four spores of a tetrad to be equally 

 loped. As a rule, one or more of the sister-spores remained very mm 

 smaller than their neighbours, and were, to all appearance, aborti^ 

 The abortion of these spores must have allowed of an inct 

 nutrition of the survivors, and thus have been of consideral 

 physiological importance. 



C alamos t achy s Casheana, Will., is the heterosporous species, 

 two specimens are at present certainly known. The general morpl 



