Equisetales. to 7 
question of the nature of the lateral strands in the bundle of 
Equisetum must be left open. 
In Schizoneura and Phyllotheca, two fossil genera from the 
Upper Palasozoic and Lower Mesozoic beds, the ribs on the stem do 
not alternate at the nodes, whereas this alternation is the rule in 
Equisetites and Equisetum. For reasons given when discussing the 
the Calamarias there can be little doubt that the latter condition 
was evolved from the former. 
In Phyllotheca the leaves of a whorl, though connected at their 
base, had free spreading limbs. The leaves of Equisetites and 
Equisetum are united into a sheath at the base, from which their 
apices only project as small teeth. This condition probably arose 
from such a one as found in Phyllotheca by the reduction of the free 
portions of the leaves. In Schizoneura the leaves are united into a 
long sheath with small projecting teeth, the sheath being split into 
two or more broad lobes. This condition may have arisen by the 
greater development of the sheath from a type of leaf like that of 
Equisetum, in which the free portions of the leaves were already 
much reduced, or more probably by the extension upwards of the 
basal fusion of the leaves of such a type as Phyllotheca. 
The strobili of the Equisetales are extremely varied. In Archaeo- 
calamites the cone consists only of superposed whorls of sporangio- 
phores ; in the recent Equisetum the cone normally consists of alter¬ 
nating whorls of sporangiophores ; in the fossil Pothocites, known only 
in impressions, the fertile whorls appear to be superposed and 
interrupted at intervals by whorls of leafy bracts ; in Calamostachys 
equi-distant sterile and fertile whorls succeed one another on the 
axis of the cone, the former alternate with one another and 
consist of twice as many members as the latter, which are said to 
be superposed to one another. In Palceostachya, fertile and sterile 
whorls consist of an equal number of members and are superposed 
to one another, the sporangiophores being inserted just above the 
bracts. In Calamostachys the vascular supply for the bract and the 
sporangiophore above it originate according to Renault (quoted by 
Dr. Scott in the course of lectures already referred to) at the same 
place on the stele, namely at the insertion of the bract. Mr. 
Hickling has shown that this is so also in Palceostachya. It might 
appear natural to those who admit the affinity of the Equisetales 
and Sphenophyllales and who regard the sporangiophores of the 
latter phylum as lobes of the sporophyll of which the dorsal lobes 
are (except in S. fertile) sterile bracts, to look upon Calamostachys 
as a form derived from Palceostachya by the shifting upwards of the 
