CARBONIFEROUS. 165 



4 inches wide. Here they are merely indicated as a point to which an 

 appendicular organ has been attached, placed on a slight oval inflation. On 

 the greater portion of this inflation the leaf-scars are preserved, showing 

 their ordinary form, and running in the same series as the other leaf -scars on 

 the stem. As the appendicular organ develops, its base pressing on the 

 outer surface of the bark eventually obliterates all trace of the leaf -scars, 

 whose presence is subsequently represented by so many little mamillse-like 

 points the extremities of the vascular bundles of the aborted leaves. By 

 the increase in girth of the stem, the bark swells up round the base of the 

 attached organ, and thus the two vertical rows of depressions are formed, 

 which keep pace in growth with the increase in size of the stem. This 

 progression I have followed through a large series of specimens. 



In 1853, Tate* clearly pointed out that the only difference between 

 Ulodendron and Lepidodendron was the presence on the former of the large 

 lateral scars. He says, speaking of Ulodendron, " specimens obtained from 

 Alnwick Moor enable us to add something to the knowledge of its form." 

 " Its internal structure is the same as that of Lepidodendron ; it possessed 

 similar leaves and rhomboidal areolae on the stem and branches. A specimen 

 in Alnwick Castle shows that its mode of branching is dichotomous like the 

 Lepidodendron, but in addition there are rows of round or oval scars on 

 opposite sides of the stem arranged vertically, and these scars continue 

 upward on the same plane along the branches, while other rows commencing 

 at the point of forking run upon the opposite side of the branches ; the scars 

 and the branches are all in the same plane. These scars appear to have 

 been the points of attachment of masses of inflorescence, which had consisted 

 of sessile cones formed of imbricated scales, in a manner similar to a fir cone. 

 The chief difference between Lepidodendron and Ulodendron would therefore 

 be that the cones, bearing sporules or seed, were placed at the end of the 

 branches on the former, but their position on the latter was in linear rows on 

 the stem and branches." This quotation contains the essence of the whole 

 subject whether the presence of lateral appendicular organs (whether cones 

 or bulbils) is a sufficient difference on which to found generic distinction. 



Stur believes that the large Ulodendroid-scars bore bulbils, but from the 

 specimen of Sigillaria (Ulodendron} Tai/lon, Carr., figured by Prof. D'Arcy 

 Thompson, I should be rather inclined to think that they bore cones, but 

 this I am unable to decide, nor does it influence the point immediately 

 at issue. 



Lepidodendron Veltheimianum did however bear terminal cones, and 

 Mr. C. W. Peach has shown me a large specimen which exhibits 22 cones 

 attached to the ends of the branches ; but this circumstance does not make it 

 impossible for Lepidodendron Veltheimianum to have also had lateral 

 appendicular organs. 



As far as the evidence goes, then, it would appear that Lepidodendron Vel- 

 theimianum had, in addition to the true terminal cones as in other species of 

 Lepidodendron, two vertical rows of lateral appendicular organs, which have 

 left behind the characteristic Ulodendroid-scars. This conclusion is founded 

 on the fact that the form and arrangement of the leaf-scars on stems showing 

 the Ulodeiidroid-scar, as well as on those which have no such marking, and 

 which constitute the Lepidodendron Veltheimianum, Sternberg, are in all 

 respects identical and cannot be distinguished from each other. They also 

 occur associated together in the same beds. The union therefore of those 

 stems, variously named Ulodendron parmatum, Ulodendron commutatum, &c., 

 with Lepidodendron Veltheimianum, seems to be an inevitable conclusion. 



There is another view of this subject, which some Botanists may be inclined 

 to take, and which must not be passed over without remark. According to 

 these the presence of the Ulodendroid-scars themselves may be of sufficient 

 importance for the creation of a distinct genus. If we accept this view, 



* Nat. History of the Eastern Borders, vol. i. p. 302, 1853. 



