The Anatomy of Lepidodendron aculeatum, Sternb. 
BY 
A. C. SEWARD, F.R.S. 
Fellow of Emmanuel College , Cambridge. 
With Plate XXVI, and Text-figures 1-3. 
A DIFFICULTY which constantly confronts the palaeobotanist is that 
only in rare instances is he in a position to supplement an account of 
internal structure by a description of external features. The absence of ex- 
ternal characters from petrified material and the lack of structure in specimens 
with well-preserved surface features necessitate the use of two series of 
specific names : the same plant must frequently be known under two designa- 
tions, one having reference to anatomical structure, and the other to external 
features. 
The late Professor Williamson wrote in his second Memoir ‘On the 
Organization of the Fossil Plants of the Coal-Measures ’ 1 : ‘ I am satisfied 
that all attempts to apply specific names to the plants of the Coal-Measures 
can but be provisional, until we learn more than we at present know of the 
effects of age upon their form and organization. Still, though they may 
not have any permanent value, such names are necessary for working pur- 
poses/ To those botanists who worked with Professor Williamson this 
statement affords but a partial reflection of the vigorous protests against the 
institution of specific names which he frequently made in conversation. 
In the case of several species of Lepidodendreae founded on anatomical 
characters we are unable to give a satisfactory account of the external 
characters: it is not only a question of correlating species founded re- 
spectively on impressions and petrifications, but the choice of a generic 
name may be a serious difficulty. 
The two genera Lepidodendron and Lepidophloios are, as a rule, easy to 
distinguish by the form of the leaf-cushions and leaf-scars, but we are not 
in a position to assign with confidence a petrified lepidodendroid stem, 
on anatomical evidence alone, to one or other of these genera, In 1894, 
1 Williamson (’72), p. 310. 
[Annals of Botany, Vol. XX. No, LXXX. October, 1906.] 
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