XV] LEPIDODENDRON 161 



Mr Watson^ that certain specimens identified by Williamson as 

 L. Harcourtii differ sufficiently from that type to be placed in 

 another species, for which Watson proposes the name L. Hickii. 



A paper on L. Harcourtii published by Bertrand^ in 1891 

 extends our knowledge of this type in regard to several ana- 

 tomical details. It was recognised by Williamson that the 

 absence of secondary wood in shoots possessing the anatomical 

 characters of L. Harcourtii is a feature to which no great 

 importance should be attached., It is possible that the large 

 stems from the Isle of Arran described by Williamson' as 

 Lepidodendron Wiinschianum, in which the secondary wood is 

 well developed, may be specifically identical with the smaller 

 specimens from Northumberland and elsewhere which are recog- 

 nised as examples of Witham's type. 



The diagrammatic sketch shown in fig. 179, A, was made from 

 a section figured by Williamson in 1893^; it has a diameter of 

 9 X 8'5 cm. The stele is of the meduUated type like that of 

 L. Wiinschianum, and the outer edge of the primary xylem is 

 characterised by sharp and prominent projecting ridges similar 

 to those of L. fuliginosum but rather more prominent. Paren- 

 chymatous cells succeed the xylem, as in other species, but in 

 this case there is no indication of meristematic activity; beyond 

 this region occur occasional patches of a partially destroyed 

 secretory zone. Remains of a lacunar tissue are seen in the 

 middle cortical region ; also numerous leaf-traces, It, consisting 

 of a tangentially elongated xylem strand accompanied by a 

 strand of secretory zone tissue enclosed in a sheath of delicate 

 parenchyma. In the inner part of the outer cortex, c\ the leaf- 

 traces lie in a space originally occupied by the parichnos; in 

 the outer portion of the same region a band of secondary 

 cortex, pd, has been formed; immediately internal to this 

 occur numerous patches of secretory tissue, represented by small 

 dots in the drawing close to pd; one is shown on a larger scale 



in fig. B. 



The position of the phellogen is seen at a; external to this 

 are radial rows of rather large cells with dark contents. 



1 Kidston (03) p. 822 ; Watson (07). ^ Bertrand, C. E. (91). 



3 Williamson (80) A. ^ Williamson (93) PL i. fig. 3. 



