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Kisch . — The Physiological Anatomy of 
confirmed by Solms-Laubach. He considers it a true periderm, derived 
from a diffuse phellogen on the inner surface, and he explains the layer of 
compressed cells, regarded as phellogen by Solms, as one of the zones of 
thinner walled, easily squashable cells which alternate with the ordinary 
prosenchyma in Z. selaginoides. 
In 1893 Hick noted the presence of a periderm zone in his new fossil 
Xenophyton radiculosum } and in the same year appeared the last of 
Williamson’s Memoirs, Part XIX, in which he brings further support for 
the conclusions of his Stigmaria monograph in the structure of a Halonial 
branch of Lepidophloios , where the ‘ meristemic zone ’ is figured between the 
outermost cortex and the prosenchyma. 1 2 Williamson again summed up 
the results of his work on the tissue in a paper for the Manchester Literary 
and Philosophical Society. 3 
Renault’s last important work was more or less contemporaneous with 
these last papers of Williamson, for the ‘Atlas ’ of his ‘ Flore fossile d’Autun 
et d’£pinac ’ was published in 1893 and the ‘Texte’ in 1896. 4 Two more 
species, Sigillaria lepidodendrifolia and Lepidodendron esnostense , are here 
described as having Dictyoxylon cortex similar to that of X. spimdosa and 
Z. rhodumnense. In 1897, Renault and Roche described another species 
preserved in the Syringodendron condition with a cortex very like that of 
Lepidodendron esnostense . 5 They considered that it had undergone suc- 
cessive decortications along the concentric zones, and that it had a true 
cork layer renewed from the inner surface, and excluding gaseous inter- 
change, which was provided for by the enlarged and persistent parichnos. 
The next important addition to the knowledge of the periderm of the 
fossil Lycopods was made in 1900 in Seward and Hill’s paper on a Lepi- 
dodendroid stem from Dalmeny (Williamson’s Z. Wnnschianuni) , which 
had a band of secondary cortex several centimetres thick. 6 This is con- 
sidered by the authors to be phelloderm, but it is not stated if there is 
any direct evidence of the position of the phellogen. The periderm is 
characterized by the presence of concentric bands of light-coloured cells., 
which are described as secretory in function. Seward and Hill are the 
first to point out the presence of intercellular spaces in the periderm of this 
species, and give more consideration than previous writers to the functions 
of the tissue, emphasizing its mechanical usefulness at the periphery. 
In 1900 was published also the first edition of Scott’s ‘ Studies \ 7 
Scott states that in Lepidodendron Harcourtii the development of the 
periderm took place on both sides of the initial layer, but he reserves the 
type of Z. selaginoides for a more detailed account of the tissue. Here 
1 Hick (14). Xenophyton is regarded by Weiss as the Stigmaria of Lepidodendron fuligino sum. 
2 Williamson (42). 8 Williamson (44). 
4 Renault (21). e Renault and Roche (23). 
e Seward and Hill (29). 7 Scott (24). 
