86. EQUISETUMS AND CALAMITES. 
and the stems are generally assumed to have been decorticated. Com- 
paring the stem of the Calamite with that, say, of E. maximum, we 
find that the external cortical layer with its lacune is wanting, the 
rest of the stem corresponding tolerably exactly. 
It is quite unnecessary for me to enter into any details as to the 
structure of Calamites, as the splendid memoir of Prof, Williamson* 
leaves little to be desired. But there are three points which seem to 
from those of all recent vaseular Cryptogams? 2. How can w 
for the stems of Calamites being so frequently decorticated ? and, 3. 
1. Is it necessary to assume that the fibro-vascular bundles in 
Calamites are differently constructed from those of all recent vascular 
Cryptogams ? 
If the description of the fibro-vascular bundles (‘‘ woody-wedges ”’) 
in Calamites given by Prof. Williamsont+ be assumed to be correct, 
then we find that their structure is essentially different from that of 
the corresponding parts in Equisetums. Nay, more, not only do they 
differ from those of Equisetums, but from those of all our recent vas- 
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ot Dicotyledons do, because, according to him, in Calamites and Dicoty- 
h place ; the bundles not being closed 
capable of regular increase by a cambium 
i setum, if the wood (xylem) portion of 
the bundle lies external to it ; and by asserting oh the a 
ternal to the lacuna, we immediately 
the fibro-vascular bundle ?—where 
a undle 
bast-portion begins, Further, it would point at once to 
the conclusion 
* Phil. Trans., 1871, p. 477, 
t Loc. cit., p. 480. 
} Williamson, op, cit., fig. 14, pl. xxiv. 
