288 MR. A. R. HORWOOD ON CALAMITES SCHÜTZEI, AND 
second short internode occurs in fertile stems, as in Æ. maximum, Е. arvense, 
Е. pratense, just before the strobilus or cone. Та barren stems this takes 
place at the internode preceding a branch-bearing period, and thence upward 
there is a decrease in length. In Æ. sylvaticum, а type in which fertile and 
barren periods are combined, a decrease first occurs in the branched period, 
then an increase, and finally just before a cone there is a further decrease. 
Where the stem is barren the internodes decrease gradually throughout the 
branched period. 
In Æ. limosum and Е. litorale some variation occurs (vide Table V, which 
should be compared with those relating to the fossil forms). 
When compared with Calamites Schiitze’, Stur *, there is seen to be a close 
correspondence in the actual length of internodes, and the relative position 
and uniform occurrence of a short internode, dividing different growth- 
periods. 
In Eucalamites and Stylocalamites the same analogy may be traced, in a 
modified form. In the former branches regularly occur on every node, and 
these are short and closely placed. In Stylocalamites, in subterranean stems 
the increase in length from the point of contact with aerial stems is strictly 
homologous with that found in the dominant type Æquisetum arvense, L. 
Where in Æucalamites the branches are few and lateral, the internodes are 
unequal and longer. The unequal or equal character of internodes may be put 
down to the position of branch-bearing nodes and the number of branches. 
Stylocalamites affords a sort of intermediate subgenus between Calamitina 
and Zucalamites, — Asterocalamites, a subgenus which is founded on entirely 
different characters, is not here considered. 
ПТ. General conclusions. 
Аз a result of the comparison made between Calamites and Equisetum it 
appears that some general principles underlie the characters noticed. 
The close correspondence here established between the position and function 
of the short (or shortened) internode and the mode of increase or decrease of 
internodes in both extinct Calamarieæ and recent Equisetaceæ constitutes 
still further evidence as to their close relationship, and it may be inferred that 
the common ancestor of the primitive Equisetales resembled them in this 
respect. 
There is, in fact, a strong resemblance between the two groups in the 
position of the short, internode, and a very marked similarity in the uniform 
rate of increase or decrease in the length of the internodes in both groups 
also, most apparent in the subgenus Calamitina, but probably in а modified 
* Stur's original figure is represented upside down. 
