470 Prof. W. C. Williamson. On the Organisation [Feb. 25, 



Apart from this general question, now conclusively settled, further 

 knowledge of L. Harcourtli has long been sought for in vain. Har- 

 court's original fragment was unfortunately an imperfect one. Its outer 

 cortex and foliage were wholly wanting, as well as specimens illus- 

 trating its various stages of growth. Recently, however, a very fine 

 series of such specimens has come into the hands of the author, and 

 a large amount of new information has been obtained from them. 

 Some of the new examples are very young branches, perfectly in- 

 vested by their bark and leaves. The detailed structures of all the 

 organs of these specimens are now described in minute detail. A 

 more exact technical nomenclature than has hitherto been employed 

 is applied to their various structures. Besides these young forms, 

 other specimens resembling that studied by Brongniart, both as 

 regards condition and apparent age, have been obtained, and also one 

 magnificent older and arborescent example, from Airdrie, in Scotland, 

 which, including all its leaves, has been between four and five inches 

 in diameter. 



But even this latter specimen presents no appearance of the 

 secondary or exogenous vascular zone so common amongst other much 

 younger Lepidodendra. Hence the author concludes that L. Harcourtii 

 has in this respect been like L. Wunschianum, the well-known Arraii 

 species, in which a magnificent exogenous zone exists, but which 

 was only developed when the plants attained to an advanced arbor- 

 escent condition. 



Some of these youngest specimens show evidence that they had 

 been fructigerous twigs. But, before describing these, the author 

 examines anew the entire subject of the branches to which the names 

 of Halonia and Ulodendron have been applied. Both of these have 

 now been proved to have been fruit-bearing branches, but their true 

 relations to each other and to their parent plants are still in a 

 state of serious confusion. The existing definitions of these two 

 types are shown to be altogether unsatisfactory ; some specimens 

 which according to one generally accepted definition are Haloniae 

 according to another are Ulodendra. In fact the two sets of 

 definitions overlap in such a manner as renders them no longer 

 applicable. 



Two classes of facts have to be considered here ; first, the positions 

 and arrangements of the reproductive fructifications on the support- 

 ing branches, and, secondly, the nature of the scars left on the 

 exterior of the bark after these deciduous fructifications fell to the 

 ground. The positions of these scars in Ulodendron are usually 

 defined as biserial, being arranged in two longitudinal rows,* one on 

 each side of the sustaining branch, whilst in Halonia these 



* In his last publication, M. Renault recognises that there are sometimes four 

 such rows. 



