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Kisch , — The Physiological Anatomy of 
the absence of rays and pits, and drew attention to the characteristic 
appearance in radial section, which he explained as due to the uniform 
length of the cells in each row. 
It was not till the work of Binney (1862-75) that the periderm of fossil 
Lycopods received any further attention, 1 with the exception of a paper by 
Dawes, in which the existence of a ‘ prosenchymatous zone’ in a Halonial 
branch was noticed. 2 Binney was the first to point out the presence of an 
‘ outer radiating cylinder ’ in Stigmaria, as well as in Lepidodendron. He 
realized the secondary nature of the periderm, but he too fell into the error 
of believing it to be a vascular tissue, a ‘ pseudo-wood 5 ; 3 and it was on 
these grounds that he based his support of Dawson’s theory that Sigillaria 
was a hard-wooded tree, and not a hollow and succulent plant, 4 though 
Dawson himself had referred only to the central axis. 5 
In 1871 appeared the first of Williamson’s great series of memoirs 
which were to do so much for the study of Fossil Botany. Memoirs II 
and III were largely devoted to the Lycopods, and already here many of 
the erroneous ideas about the periderm were dispelled. From the first 
Williamson gave no support to the vascular theory. f If I am correct in 
these determinations,’ he writes in Memoir II, ‘no question can arise as 
to the cortical nature of the thick, investing, and more external layers.’ 6 
Towards the end of Memoir III fossil periderm is compared for the first 
time to the cork of recent plants. ‘ I have got some magnificent specimens 
of bark,’ says Williamson, * which show that the two outer layers ... in- 
creased in thickness through a meristem action. . . . Hence, we appear to 
have two concentric vertical zones in which these alternations occurred, 
one . . . the true cambium layer, and the other in the same plane as that 
which contributes to the growth of the cork-layer of the bark.’ . . . 7 
In 1875, three years after the publication of Memoir III, appeared the 
memoir on Sigillaria spinulosa by Renault and Grand’Eury, 8 and this 
included a fairly detailed description of its peculiar Dictyoxylon cortex, as 
it appears in transverse and longitudinal sections. Three years later, 
Williamson, in his ninth Memoir, described what he thought was an English 
example of the same species, 9 and showed that the cells of the meshes were 
in a state of active division, and that there were signs of similar activity in 
the peripheral parenchyma. He also brought forward a theory as to the 
origin of the tissue, viz. that it was developed from a meristematic layer on 
the exterior ; while in function he considered it similar to the ‘ phellem 
layer of living exogens \ 1Q 
1 Binn ey ( 4 ), ( 5 ), (6), ( 7 ). 
3 Binney ( 5 ), p. 592. 
6 Dawson (10). 
7 Williamson ( 38 ), pp. 313-14. 
9 It was really a Stigmaria. 
2 Dawes ( 9 ). 
4 Binney ( 5 ), p. 597. 
6 Williamson ( 37 ), p. 203. 
8 Renault and Grand’Eury ( 22 ). 
10 Williamson ( 39 ), p. 355. 
