$ WATSON, Two Species of Lepidodendron Harcourtii. 



These tracheids are of almost uniform diameter, about 

 016 mm. 



Longitudinal sections shew that the great mass of 

 the primary wood consists of scalariform tracheids. 



In these tracheids the vertical threads between the 

 bars, once regarded as diagnostic of L. Mundum, Will., 

 are well seen. 



These threads have been seen in BotJirodendron = 

 Lepidodendron Mundum (Will.), L. Wunschianum, Will., 

 L. vasculare, Binney, L. brevifolium, Will.,* L. squamosum, 

 Gopp., and Stigmaria ficoides (Seward, :00, p. 910). Their 

 occurrence in L. Hickii is noted by Williamson, who states 

 that they are not seen in older branches of L. Harcourtii ; 

 they do, however, occur in a section (A 193 of my own 

 collection) of L. Harcourtii from Shore roof. 



The occurrence of these threads thus seems to be a 

 constant character in the Lepidodendraceae, and the 

 explanation given by Solms-Laubach ('92, p. j6) and 

 Seward ('99) that they are the remnants of the pit-closing 

 membrane seems to be the true one. 



(3) Phloem. 



The soft tissues of the stele external to the wood are 

 in no case well preserved (best in the series A 169, 170, 

 171 in my own collection)-! {Fig- 2, Plate I.) 



Immediately surrounding the wood is a belt of small 

 celled parenchyma about 5 cells or # o8 mm. broad {Fig. 7, 

 Plate III.) 



* I use the name L. brevifolhtm of Williamson for the Lepidodendron of 

 Burntisland, because the occurrence of typical Lepidophloios leaf bases in the 

 material suggests that the identification with L. veltheimaeanum may not be 

 always true. 



t This illustrates an interesting point in connection with preservation. 

 The preservation of histological details is bad in this series, which shows 

 more of the phloem and middle cortex than any other, whereas the section 

 A 144 with fine histological detail, has lost all its soft tissues. 



