of Ulodendron to Lepidodendron, &g. 135 



that which occurs in recent Lycopods, where the little cones 

 are only modified branches. These modified branches, he 

 believes, resulted in the formation of short-stalked cones ; and 

 he mentions the following objections to Star's opinion that 

 the appendicular organs were detachable bulbils : — 1st, that 

 when bulbils occur in the Lycopodiacese they are axillary, and 

 when shed leave behind them no scar on the branch ; and 2nd, 

 that they never show the regularity in position that is shown 

 in the scars of Ulodandron. Schimper here still regards 

 Ulodendron as a true genus, and appears to think that the 

 union of Ulodendron Siwd. Le2ndodendron\'e\m.m^ to be proved. 

 He admits that Lepidodendra commonly occur with Uloden- 

 dra^ but can be distinguished from the last-named genus by 

 their larger leaf-scars and the absence of the Ulodendroid 

 scars. 



1880. Thomson, D'Arcy W. " Notes on TJlodeyidron and 

 Halonia^^ (Trans. Edinb. Geol. Soc. vol. iii. partiii. p. 341). 

 — This writer enters into a general discussion as to the affini- 

 ties and structure of these plants. The conclusions he arrives 

 at are : — 



" 1st. That the scars of TJlodendron and Halonia^ though 

 unequally developed, have similar significance. 



" 2nd. That these scars were points of attachment for the 

 organs of fructification, and that these organs were cones or 

 spikes, thicker and probably shorter than those of Lepido- 

 dendron. 



" 3rd. That in Ulodendron the cone was attached only to 

 the central point of the scar ; that the rest of this areola was 

 originally covered with leaves after the fashion of the remain- 

 ing portions of the stem ; but was subsequently moulded by 

 the process of growth on the lower surface of the cone. 



" 4th. That the oval form occasionally presented by the 

 scars of Ulodendron is in all cases the result of secondary 

 causes, and that this and the other slight modifications of shape 

 and surface-markings in the scars are valueless as specific dis- 

 tinctions. 



" 5th. That the leaves of Ulodendron were small, narrow, 

 lanceolate, and imbricate after the ordinary Lepidodendroid 

 type, and that both Halonia and Ulodendron branched by 

 repeated dichotomy in the usual characteristic manner. 



" Finally, That Ulodendron and Halonia were closely 

 allied Lepidodendroid plants ; that on presumptive evidence 

 Prof. Williamson's suggestion may still be retained, viz. that 

 Ulodendron and the biserial ' Halonice ' may possibly repre- 

 sent portions of one and the same form ; and that, in this 



