Mr. B,. Kidston on Ulodendron, &c. 239 



XXIV. — On the Relatio7iship of Ulodendron, Lindley and 

 Hutton, toLepidodendron, Sternberg ; Bothrodendron, Lindlei/ 

 and Hutton ; Sigillaria, Brongniart ; and E/lijtidodendron, 

 Boulay. By ROBEET KiDSTON, F.Gr.S. 



[Plates ni.-VII.] 



[Concluded from page 179.] 



It is necessary before leaving this portion of our subject 

 to make a few remarks on the Ulodendroid scars. It haJs 

 been stated by some authors that the large concave Ulo- 

 dendroid scars bore traces of leaf-scales ; by others that these 

 were never present. It is, hov^ever, now unquestionable that 

 at one period of their development the whole area which now 

 forms the Ulodendroid scar was covered with leaf-scales. 

 This is clearly shown in PI. IV. fig. 2 (specimen No. 3), and 

 in another and slightly older example (specimen No. 7). It 

 has also been stated, by those who believe that the surface of 

 the Ulodendroid scars originally bore leaf-scales, that these 

 were arranged in a system peculiar to the area of the scar. 

 At all events in the two examples just mentioned the leaf- 

 scars on the surface of the Ulodendroid scars are continuations 

 of the ordinary leaf-spirals of the stem. The presence^ then, 

 of the leaf- scars on the Ulodendroid scar conclusively proves 

 that the appendicular organ, whatever its nature may have 

 been, cannot have been attached to the whole surface of the 

 scar, but only to its umbilicus. Further conclusive proof of 

 this is afforded by the Blackbraes specimen (No. 6) of Lepi- 

 dodendron VeltJieimianum . (PI. VI. fig. 11.) 



The formation of the Ulodendroid scar may be thus briefly 

 described. In its earliest condition that has come under my 

 notice the area that supports the appendicular organ is slightly 

 elevated (PI. IV. fig. 2). The specimen (No. 7) which shows 

 the succeeding stage of development exhibits a clearly defined 

 semilunar outline, limiting the upper part of the scar, but no 

 boundary-line towards its lower part is yet visible. At this 

 stage of progression the leaf-scars are clearly seen on the 

 surface of the Ulodendroid scar, from the umbilicus down- 

 wards. 



Fig. 9, PI. V. {Sigillaria Taylori)^ shows the attached 

 appendicular organs in a young state of growth. They are 

 directed upwards, and consequently the pressure exerted on 

 the bark by their leaves or bracts will be much greater on the 

 upper part of the Ulodendroid scar from the acute angle the 

 attached organ forms with the stem ; and, in fact, it is on the 



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