722 PROFESSOR W. C. WILLIAMSON AND DR. D. H. SCOTT ON THE 
acquired character. It is highly probable that they still retained the mode of 
growth characteristic of plants which are destitute of secondary thickening. In 
like manner Dracana or Aristea resembles any other Monocotyledon in the earlier 
stages of its development though it ultimately forms secondary tissues.* 
The very small stems with a normal pith and separate bundle (see “ Organization,” 
Part XVII, Plate 14, fig. 12) remain unexplained. They are not connected by 
any clear intermediate forms with the typical specimens, yet it is impossible to doubt 
that they belong to Lyginodendron. ‘Their xylem elements are decidedly smaller 
than those of the ordinary stems, but the latter vary so much among themselves in 
this respect, that we cannot attach much importance to such differences. Stems of 
this kind must apparently represent some kind of lateral axis, which has not yet 
been found in connection with the main stem. The somewhat deficient formation of 
sclerenchyma suggests that they may have been weak runners or subterranean shoots. 
8. Structural Anomalies. 
So far we have concerned ourselves with the normal structure of the Lyginodendron 
stem, such as is common to a majority of the numerous specimens investigated. 
Some interesting departures from this typical anatomy occur in individual specimens. 
The most remarkable and perhaps the most frequent of these anomalies depended on 
the appearance of a secondary meristem at the outer border of the pith. In some 
stems this medullary meristem gave rise merely to secondary parenchyma, with some- 
what thickened walls; in other cases, however, it acted as a regular cambium, 
producing medullary wood and bast with inverted orientation. In the latter case, we 
have precisely the same anomaly as in Tecoma, Jodes, or Acantholumon among recent 
plants. It is a most remarkable fact, that this peculiarity should have already 
appeared as an occasional variation ina carboniferous plant, so absolutely remote from 
the Dicotyledons as is Lyginodendron. A more striking warning against the indis- 
criminate use of, even conspicuous anatomical characters cannot be imagined. Such 
a warning, it is true, is not needed by those who have experience in anatomy. The 
anomaly in question is known to be of very inconstant occurrence at the present day. 
Both in the genera, Tecoma and Jodes, some species show it and others do not, 
though analogous peculiarities (internal phloém for example) are often characteristic 
of entire natural orders. Anatomical characters, in fact, like any other characters, 
are sometimes of great constancy, sometimes highly variable, while the same 
character, which is relatively constant in one family may be most inconstant in 
other groups. 
In the present paper, we have been compelled, in the absence of organs of fructification, 
to make great use of anatomical characters. We have, however, endeavoured to rely 
* The following slides show a more or less continuous xylem-ring:—C.N. 1137, 1150 (“ Organization,” 
Part IV., Plate 22, fig. 2); 116], 1885 H (“‘Organization,” Part XVII., Plate 13, fig. 11); 1915 N, 
1915 R. 
