74 THE AMERICAN NATURALIST. [VoL. XXXV. 
The plants dealt with are, for the most part, the vascular Palzo- 
zoic plants, — Pteridophytes and Gymnosperms, — but some space 
is also given to the Mesozoic types. 
The first chapter is partly devoted to an exposition of the aims of 
palzobotany and explains the different forms in which fossil plants 
have been preserved; the latter part of the first chapter and the two 
following are devoted to the Equisetales. 
The earliest forms of Equisetales (Archzocalamites) occur in the 
upper Devonian. These oldest types were in many respects allied 
to the sole living genus, Equisetum. From this stock arose the 
much more specialized Calamites of the Carboniferous, which showed 
a secondary growth of the vascular bundles and more specialized 
fructifications. The peculiar fossils described under the name 
* Annularia " are supposed to be the smaller leafy twigs of Calamites. 
The structure of the latteris often preserved most beautifully and 
shows great similarity to that of Equisetum, with which the spo- 
rangia also have much in common. The discovery of heterospory 
in certain species is an interesting point, but it was apparently much 
less marked than among the Lycopods and Ferns. Dr. Scott is very 
positive in maintaining the strictly pteridophytic nature of all the 
Calamariez. No Calamites are found above the Permian, the Meso- 
zoic Equisetales being for the most part closely allied to Equisetum. 
Chapter IV deals with the Sphenophyllales, which Dr. Scott con- 
siders are entitled to rank as a fourth class of the Pteridophytes, 
having certain affinities with both the Lycopods and Equisetales. 
Of existing genera, Psilotum approaches Sphenophyllum in the 
character of the vascular bundles, but as practically nothing is 
known of the fossil Psilotacez, it is questionable how close the 
relationship really is. 
e very remarkable fructification known as Cheirostrobus, which 
apparently combines calamarian and lycopodiaceous characters, is 
considered by Dr. Scott to belong to the Sphenophyllales and to 
confirm his view that “the Sphenophyllales were the highly modified 
representative of an ancient stock from which both Lycopods and 
Horsetails have diverged." 
Chapters V-VII deal at length with the very abundant remains 
of Lycopodiales. As was the case with the Equisetales, the group 
culminated in the Palzozoic era, and in the later formations only 
the smaller and less specialized types are encountered. Hetero- 
spory, which still occurs in Selaginella, was very pronounced, and in 
the case of certain forms closely resembling typical Lepidostrobus, 
