110 Dr. Dawson on an Erect Sigillaria 



are illustrated in my paper on the South Joggins section. Speci- 

 mens which I have observed, however, as well as facts stated by 

 Mr. Brown and by Brongniart, induce me to believe that in some 

 species this mode of growth was so far modified that new ribs 

 were introduced to the very base of the trunk. The expansion of 

 the trunk was accompanied by the flattening out of the ribs, and 

 also by the giving way of the thin outer bark, the inner or middle 

 bark evidently remaining in a growing state lo the base of the 

 stem. 2. The decadence of the leaves from the lower part of the 

 trunk in the living state, is proved by the condition of the scars. 

 We may also note the shorter vertical distance of the scars 

 on the lower part of the trunk, showing that, when young, 

 the leaves were much more crowded than subsequently : and 

 the absence of bands of deformed and crowded scars sometimes 

 seen on Sigillarice^j probably connected with periods of fructifi- 

 cation, and possibly occurring on the upper part of the trunk only. 

 3. The difficulty of comparing the characters of erect with those 

 of prostrate Sigillarioe; the former usually showing only the base of 

 the stem, the latter often only the upper part, and these differing 

 so materially that they may be mistaken for distinct species. 4. The 

 mode of growth illustrated by the specimen may apply only to a 

 portion of the plants usually included in the genus. The spe- 

 cies of Sigillaria found at the Joggins may amount to about 

 twenty ; and with reference merely to the habit of growth, with- 

 out regard to the resemblances or differences in the leaf-scars, 

 these may be arranged in three groups. The first will include 

 the present species with S. reniformis^ S. alternans, S. organumj 

 and another [S. ovalis, mihi) with oval scars like those of S' ca- 

 tenulata but an inch apart vertically. These have broad and well- 

 marked ribs, attain to a large size, and often occur erect. Other 

 species with narrow and less distinct ribs and more or less crowd- 

 ed scars, as S. elegans, JS, Knorrii, S. scutellata, S. Saullii, (fee, 

 do not appear to have attained to so great diameter, and are 

 more rarely seen erect. In some of these species the markings 

 and leaf-scars seem to be more perfectly preserved to the very base 

 of the trunk than in the species before mentioned. A third group 

 consists of species like S. De/ranciij S. Menardiij &c., which are 

 destitute of ribs and have the scars arranged spirally. Some of 

 these were of considerable diameter, others quite small ; but they 

 are rare, and I have not recognized them in the erect position, 



* Ibid. vol. xv. p. 640. 



