THE VEGETABLE KINGDOM 33? 



so much that they have been put into distinct geriera 

 belong to stems which cannot be distinguished, and 

 again stems which seem justifiably to be divided into 

 two or more genera have indistinguishable roots. A 

 triplicate nomenclature at least is therefore inevitable, 

 and palaeobotanists speak of " leaf-genera," etc. In the 

 case of the most fully investigated Coal- Measure plant, it 

 is known that at least five generic and five trivial names 

 had been given to its separate parts. 



Sphenophyllales. Only one genus is known, Spheno- 

 phyllum (Dev. ? Carb. L. Perm.), which seems to have 

 been a climbing plant, very much like the modern bed- 

 straws in appearance. The leaves are in whorls round 

 the stem, and are wedge-shaped, narrow at the attachment, 

 widening out and ending abruptly at their broadest. 



Equisetales. This group attained its highest develop- 

 ment in the Carboniferous period, when it was represented 



FIG. 100. FOSSIL PLANTS. 



a, Solenopora compacta (Billings), Ordovician. a, Vertical section (X25), 

 showing part of three concentric layers of cells. a', Horizontal 

 section. (X5O.) (After Brown.) b, Chara lyelli Forbes, Oligocene. 

 Fruit. (Xio. ) (After Forbes.) c, Sphenophyllum schlotheimi Brong- 

 niart, Coal Measures, c, Stem with whorls of leaves. (X.) 

 c' , single leaf. (Natural size.) d, Lepidodendron sternbergi Brong- 

 niart, Coal Measures. (Xj.) d', Leaf-traces of L. gracile Lindley. 

 (X^.) e, Sigillaria tessellata Brongniart, Coal Measures, e, Part of 

 trunk (X.) e', Leaf- traces. (X.) /, Calamites mougeoti Brong- 

 niart, Coal Measures. Trunk. (X,.) /', C. decoratus Brongniart, 

 Coal Measures. Bark. (Xj.) g, Neuropteris heterophy lla Brongniart, 

 Coal Measures. Part of leaf. ( X J). g*, Venation of N. blissi 

 Lesquereux. (X.) (After Kidston.) h, Alethopteris lonchitica 

 (Schlotheim), CoallMeasures. Leaf. (x.) ti, Leaflet. (Natural size.) 

 To show venation, z, Glossopterisbrowniana Brongniart, Permo-Carbo- 

 niferous, New South Wales. Leaf. (Xj.) i', Venation. (Xf.) 

 (After Seward. ) j, Williamsonia pecten (Phillips), Lower Estuarine 

 beds (Aalenian), Scarborough. (Xj.) (After Seward.) k, Ginkgo 

 digitata (Brongniart), Middle Estuarine beds (Bajocian), Scarborough. 

 (X^.) (After Seward.) (After Brongniart or Lindley, where not 

 Otherwise stated.) 



22 



