GENERAL RESULTS— SPHENOPSID A 619 



delicate tissues are preserved and a great variety of 

 organisms represented. The question of the existence 

 of Palaeozoic Bryophyta must still be regarded as an 

 open one. The hypothesis that the Pteridophyta arose 

 from a Bryophytic ancestry has thus received no 

 support from the palaeontological record. 



We will now go on to consider, somewhat more 

 fully, the affinities of the various groups of Vascular 

 Plants dealt with, beginning with the articulated 

 Sphenopsida. 



Sphenopsida 



The general morphological agreement between 

 the two classes Sphenophyllales and Equisetales is 

 manifest, and extends to Nathorst's new class Pseudo- 

 borniales. The articulated stem, and the constant 

 verticillate arrangement of the appendages, are 

 characters obviously common to the whole series. 

 Archaeocalamites , the oldest of the known Equisetales, 

 distinctly approaches the Sphenophyllales in the 

 superposition of the verticils and in the dichotomously 

 divided leaves, while in many Calamariaceae the in- 

 dividual leaves resemble the leaves or leaf-segments 

 of the plurifoliate Sphenophyllums so closely as to 

 be almost indistinguishable. Professor Lignier has en- 

 deavoured to carry the comparison further and to place 

 it on an anatomical basis. In the typical species of 

 Sphenophyllum there are six leaves in a whorl, but the 

 vascular strands supplying each two leaves start from 

 the same angle of the triarch stele, suggesting that three 

 was the original number of leaves in a verticil. In some 



