626 STUDIES IN FOSSIL BOTANY 



Equisetales, it is an interesting question whether our 

 living Equiseta are their degenerate descendants, or the 

 offspring of a simpler stock which may have co-existed 

 with the arborescent forms in ancient times. The earlier 

 Mesozoic Equisetales appear to have been intermediate 

 in certain respects between the Calamariaceae and the 

 recent genus, as shown especially by Mr. Halle's results 

 (p. 83). By Wealden times, forms almost identical 

 with modern Horsetails had appeared. These facts 

 favour the hypothesis of reduction, which may also be 

 supported by the observation (if rightly interpreted) 

 of secondary growth, at the nodes of some living 

 Equiseta. 1 The Equisetales, as a class, have con- 

 spicuously failed to hold their own in the secular 

 struggle for existence, though the survivors are 

 extraordinarily well adapted to particular conditions, 

 and maintain their ground, when once established, 

 with singular obstinacy. 



The possibility of a relation between the Sphen- 

 opsida and the Lycopsida will be discussed under the 

 latter head, but we have now to consider the reasons 

 for including the recent group Psilotaceae in the same 

 division with the Articulatae. The question concerns 

 us here because it turns entirely on the relations 

 between the recent family and the Palaeozoic class 

 Sphenophyllales. The points of comparison of chief 

 importance are the anatomy of the stem and the 

 morphology of the sporophyll. As regards the 

 former, Psilotum presents a nearer analogy with 

 Sphenophyllum than any other living plant • the 

 resemblance becomes very marked in those branches 



1 Cormack, Annals of Botany, vol. vii. 1893, p. 63. 



