104 
Lady Isabel Browne. 
following quotation will show : “ On the whole considering the age of 
Archaeocalamites and the few characters with which we are 
acquainted, it is probable that this genus is very closely related to 
the typical Calamites, and may be regarded as a type which is in 
the direct line of development of the more modern Calamite” (16) 
Professor Seward also quotes cases of irregular superposition in 
Calamites and irregular alternation in Archaeocalamites. As in 
Grand ’Eury’s Permian Autophyllites the ribs of the stem did not 
usually alternate there appears to be some variety in the course 
of the vascular bundles, probably indicating that the transition from 
superposed to alternating bundles took place fairly easily. 
In Archaeocalamites the leaves were dichotomously divided and 
Professor Lignier seems to have proved that, as in the Spheno- 
phyllaceae the numerous simple leaves of Calamites represent the 
segments of a smaller number of compound leaves (8). Dr. Scott 
has fallen in with this suggestion (15). The process of multiplication 
by precocious division of the trace within the tissues of the stem 
seems to have been carried further in Calamites than in Spheno- 
phyllum, for the leaves are very numerous and uni-nerved; this 
might lead us to suppose that they represent ultimate pinnules. In 
Autophyllites we have a stage which is perhaps intermediate between 
Archaeocalamites and Calamites, for the leaves are once forked at 
their apex only. Owing to the great increase in the number of the 
leaves the numerical proportions were probably lost. We may 
still, however, see a trace of this origin by division of a smaller 
number of leaves and their vascular supply, for in the axes of the 
cones of some species of Calamostachys and Palceostachya (genera 
founded on Calamarian cones) though the members of each whorl 
are equi-distant their bundles are still grouped in pairs round the 
cauline stele, thus suggesting the origin of the numerous members 
of a whorl by the sub-division of a smaller number. The repro¬ 
ductive axis would then be more primitive than the vegetative one. 
Leaving aside for the present the consideration of the cones of 
the Calamariae, we will briefly consider the vegetative features of 
the Equisetaceae. As here understood this order cannot be asserted 
to be a natural one, for it includes the two fossil genera, Phyllotheca 
and Schizoneura, known only as impressions, whose position in the 
phylum it is difficult to estimate justly. Equisetites is also only 
known in impressions, but its similarity to Equisetum leaves no 
doubt of its close affinity with that genus. The stem of Equisetum 
contains a ring of collateral vascular bundles surrounding a pith. 
The most striking anatomical differences found within the genus 
