PRESENT POSITION OF PALEOZOIC BOTANY—SCOTT. 379 
took place under these conditions as we actually find in Calamos- 
tachys there would be a near approach to the /quisetum arrangement. 
Taking all the characters, vegetative and reproductive, into account, 
the affinity of the Equisetales with the wholly Paleozoic group 
Sphenophyllales may be regarded as established. Archwocalamites, 
though it shows some approach to the Sphenophyllales, is none the 
less a manifest Calamarian, while in Cheirostrobus the Spheno- 
phyllaceous characters as evidently predominate. Psewdobornia is 
probably, in the present state of our knowledge, best kept in a dis- 
tinct class, as Nathorst proposes though perhaps it has the strongest 
claims of any known genus to be called a Protocalamarian. 
III. PSILoTALEs. 
It is not my purpose, under the above heading, to discuss the 
highly doubtful fossils, such as Psilophyton and Gomphostrobus, 
which have sometimes been referred to the Psilotaceze, but rather to 
consider the affinities of the recent group in the light of our knowl- 
edge of the Paleozoic Sphenophyllales. The two points on which 
the question turns are the anatomy of the stem and the morphology 
of the sporophyll. As regards the anatomy, Psilotum presents a 
nearer analogy with the Sphenophyllales than any other recent plant, 
the resemblance being most marked in those branches where the stele 
is triarch and the xylem extends to the center. The discovery by 
Boodle that, at the base of the aerial stem and in adjoining parts of 
the rhizome of Psilotum, a well-marked formation of secondary wood 
may take place in old plants, strengthens the anatomical analogy in 
a striking manner. 
Still closer is the anatomical resemblance in the reproductive 
organs. For example, in 7’mesipteris (the less reduced of the two 
genera of Psilotaceze) the development and ventral position of the 
pedicellate synangium and the anatomical relation of the latter to 
the subtending sporophyll correspond exactly to the conditions in 
the Sphenophyllales. The repeated dichotomy of the sporophylls, 
discovered by Professor Thomas, which is so frequent as clearly to 
fall under the head of normal variations, certainly appear to be 
fatal to the idea of any near affinity between Psilotales and the 
Lycopods, while it strongly supports a relationship to the Spheno- 
phyllales rather than to any other group. This relationshp also 
explains the normally forked sporophyll of Pstlotuwm and T'mesip- 
teris; it may well represent the dichotomous form of leaf so 
common in Sphenophyllum. There can be no doubt that on the 
whole of the evidence there is a good case for the Sphenophylla- 
ceous affinities of the Psilotacee. The arguments on which the 
comparison of this group with the Ophioglossee have been based 
apply with far greater force to the Sphenophyllales, and are sup- 
