ORGANIZATION OF THE FOSSIL PLANTS OF THE COAL-MEASURES. 723 
on those which are known to be of great persistency in families which presumably 
belong to the same cycle of affinities as the plants with which we are dealing. 
Characters dependent on the activity of the cambium are perhaps peculiarly liable 
to variation. Whenever a plant has acquired the power of secondary tissue-formation, 
all the anomalies, even of the most abnormal Dicotyledons become possible; in 
Lyginodendron some of these possibilities are actually realized. 
We do not find the slightest reason to believe that the anomalous medullary 
cambium of Lyginodendron was a character even of specific value ; among stems, which 
are perfectly similar in other respects, some show it and some do not, while in those 
that possess this anomaly, the degree in which it is developed is most variable. 
A characteristic example of the formation of anomalous medullary wood and bast 
has been previously figured.* 
Our fig. 8 (Plate 23), from another section of the same stem, shows plainly that 
there is a true cambium on the medullary side of the primary bundles, giving rise to 
secondary xylem on its outer side, and to secondary phloém towards the interior. The 
figure cited from Memoir XVII. demonstrates an interesting point, confirmed by other 
specimens, namely, that the anomalous medullary tissues extend through the leaf-trace 
gap along the sides of the normal secondary wood. In the section from which this 
figure was drawn, the zone of secondary wood is sub-divided by parenchymatous trace- 
gaps into four masses, each of which is completely surrounded by cambium. We 
have, in fact, in this case precisely the anomaly described by DancEarp in Acantho- 
phyllum.t It is probable that the new cambial divisions spread from the normal 
cambium through the parenchyma of the leaf-gaps into the pith, just as Roprnson 
found to be the case in Jodes tomentella.{ Thus in another stem, from which fig. 9 
was drawn, there is a small amount of anomalous wood (x) behind the outgoing trace 
figured. The anomalous trachez found at the edges of the leaf-trace gaps sometimes 
have a horizontal course (“‘ Organization,” Part XVII, Plate 13, fig. 3). 
In one or two instances, where the anomalous tissue is mainly parenchymatous, the 
internal cambium appears to have arisen partly from the parenchyma of the primary 
xylem, so that some of the trachez belonging to the latter have been carried inwards 
into the pith.§ We omit one or two specially complicated forms of anomalous 
medullary tissues, which are of isolated occurrence.|| 
* “Organization,” Part 17, Plate 13, fig. 3. The cabinet contains four sections of this specimen, 
C.N. 1138, 1142, 1190, and 1885E. 
+ Danczarp, “ Monographie Anatomique des Acanthophyllum ;” ‘Le Botaniste,’ 1889. 
¢ Rosiyson, “On the Stem-structure of Jodes tomentella, é&c.,” ‘Annales du Jardin Botanique de 
Buitenzorg,’ vol. 8, 1890. 
§ C.N. 1114 and 1118. One of us found a similar mode of development in Acantholimon (see Scorr 
and Brebyer “ On Internal Phloém in the Root and Stem of Dicotyledons,” ‘Annals of Botany,’ vol. 5, 
1891, p. 296.) 
|| The following specimens in the WritLtAmson collection show anomalous tissues in the pith: 
C.N. 1114, 1118, 1138 and other sections of the same stem ; 1153. 
5 A 2 
