494 PROF. PERCY GROOM ON THE 
The forms of the Internode-curves I., IT., IIT. show that those parts repre- 
senting the respective cycles (or periods) in each specimen largely agree in 
general form and regularity. 
En passant it may be noted that the commencement of Curve П. shows 
that the stem of Calamitina varians could increase in length in one season by a 
number of millimetres much larger than 125 millimetres. Calamites Schützei 
and C. undulatus show increments in length of 240 and 376 millimetres 
respectively in one season. These statistics, though interesting as giving, 
for the first time I believe, an estimate of the rate of growth in length of 
fossil stems, obviously tell us nothing of the mean or maximum rate of 
Curve II. 
Calamatina varians, var. inconstans : measurements are in millimetres. 
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A МУ 
м. Mt 
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M. 
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growth of the species. The other measurements supplied by Kidston, 
Jongmans, and others, are not sufficiently numerous to allow of comparison 
of two or more cycles. 
II. Insertion of the Branch-scars, and their dimensions. 
In the specimens of which measurements have already been given here, 
the correspondence between the position of the branch-sears and. the length 
of internodes is obvious. According to the scheme here presented, the branch- 
scars occupy the same position as strongest buds or branches of trees. This 
scheme is nearly certainly correct for Calamitina varians, the other alterna- 
tive being the occurrence of two internodes above the insertion of the branch, 
The matter is more doubtful in the cases of Calamites Schiitzei and Calamites 
