May, 1893. THE FRUIT-SPIKE OF CALAMITES. 355 
is only partially given. Among other details, however, it is stated 
that the axis had “a bundle of fine scalariform tissue in its centre, 
forming about a third of its diameter, and generally appearing free 
from the surrounding cellular tissue, which is composed of somewhat 
elongated cells.” 
Throughout his description, Carruthers appears to have had no 
doubt whatever that he was dealing with the fruit of Calamites. In 
this he was probably guided by the great and undoubted similarity 
of the general characters of the spike to those of Eguisetum, with 
which Calamites has always been held to have a close relationship. 
At any rate, he does not seem to have considered that the anatomy 
of the axis as he then understood it, 7.e., with scalariform tissue, 
and not parenchyma, in the centre, was an insuperable difficulty in 
the way of a determination supported by so many of the other 
characters of the spike. 
Binney’s description of Calamostachys Binneyana was published in 
1868, and though his account is very unsatisfactory from the 
botanist’s point of view, it implied the presence of a vascular bundle 
in the centre of the axis, as described by Carruthers. In spite of this, 
he accepted the view that the affinities of the spike were with 
‘Calamites, and does not seem to have considered it necessary to explain 
on this assumption the presence of the axile vascular strand. 
In 1871 Williamson began that series of memoirs on “ The 
‘Organisation of the Fossil Flora of the Coal-measures’”’ which have 
done so much to increase our knowledge of Carboniferous plants. 
The first of these deals with Calamites, and incidentally the question 
of its relationship to Calamostachys Binneyana is referred to. It is 
pointed out (5) that in Calamites the centre of the stem is occupied by 
a purely cellular pith with a vascular zone at its periphery, while in 
Calamostachys Binneyana these conditions are reversed. Hence the 
inference is drawn that if the latter be the fruit-spike of the former, 
then in passing from one to the other the tissues must undergo a 
metamorphosis which is without parallel among living plants. In 
the fifth memoir (1874) the spike is described afresh, and many 
new details of structure are given with respect to it. Discussing its 
affinities in the light of the fuller knowledge, the author says (6) :— 
‘«« After balancing these various facts and arguments, I am led to 
the conclusion that Calamostachys Binneyana has much closer affinities 
with A stevophyllites than with Calamites. With the latter it has no one 
feature in common. There is no solitary point in which the two 
plants resemble each other. The resemblance of the fertile sporangia 
of Calamostachys to those of Equisetum has been combined with the 
foregone conclusion that the Calamites were Equisetaceous plants, in 
leading to the belief that the two were parts of the same plant; but I 
cannot conceive of any conditions in which the stem of a Calamite 
could be prolonged into that of a Calamostachys. I have carefully 
investigated the relations which the fertile stems of the Equiseta bear 
to axes of their terminal fruit-spikes, and I find that their respective 
structures are typically identical. The transition from the stem to 
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