Vol. 63.] XEROPHYTIC CHARACTERS OF COAL-PLANTS. 285 



to certain modern types, especially the Marattiece, whether they 

 were humble plants or trees ; and, as existing ferns grow in 

 widely-different situations, such as the purely-hygrophytic Hymeno- 

 phyllum and the intensely-xerophytic Ceterach on dry walls and 

 rocks, we may expect to find a considerable range in fossil forms 

 as well. 



With regard to groups more or less intermediate in character, 

 such as the Cycadqfilices and Cordaitce, they are decidedly xero- 

 phytic. Similarly the Lycopodiales, like our existing representative 

 Lycojpodium, bear unmistakable xerophytic characters in different 

 degrees ; as, for example, in the usually total absence of lacunas, in 

 the great development of wood and sclerenchyma, in the closely- 

 imbricated and coriaceous leaves, and in the numerous layers of the 

 palisade-tissue, of the latter. 



In fine, excepting the Equisetales, the characteristic features of 

 the great majority of the coal-forests appear to have been such 

 as must be looked for in an upland flora, rather than in marshes. 

 This is an important fact, for the geological problem is : How came 

 upland forests to form coal, hundreds if not thousands of feet below 

 the present surface ? 



Before replying to this question, a few illustrations will be 

 desirable to show .the differences between the hygrophytic and the 

 xerophytic characters. The figures in Dr. D. H. Scott's ' Studies 

 in Fossil Botany ' 1900, will answer the purpose. 



Calamites and Calamodendron (figs. 4, 5, 10, & 12, pp. 19, 20, 33, 

 & 36) show a lysigenous lacuna at the apex of each vascular bundle 

 of the stem. Pig. 6 (op. cit. p. 22) shows, by a radial section of 

 the bundle, how the lacuna is formed by the disorganization of the 

 spiral or scalariform vessels. This occurs in living plants. Figs. 14 

 & 15 (pp. 39 & 42) exhibit large, schizogenetic, regularly-formed 

 lacunae in roots separated by trabecule, in the cortex. Both kinds 

 of lacunas are common in all existing aquatic and semi-aquatic 

 plants. On the other hand, there is a total absence of all kinds 

 of sclerenchyma, so eminently characteristic of xerophytes. 



Comparing the above with the anatomy of species of living 

 Equisetum, such as E. arvense and E. maximum, the latter exhibits 

 precisely the same kinds of lacunae, namely, at the apex of the vascular 

 bundles and in the cortex. E. arvense, on the other hand, having 

 become a land-plant, has adapted itself by adding silicified fibrous 

 strands on the circumference of the stem, while retaining the 

 hydrophytic feature of lacunae. 



It may be advisable here to add a few words on adaptations. 

 A plant may have been, for many generations, either a xerophyte 

 or a hygrophyte, but if its spores or seeds reach a district of an 

 opposite character, they germinate and respond to its influences, 

 forming adaptive features ; so that it is of common occurrence to find 

 both kinds of structure in one and the same plant, as in E. arvense. 

 Indeed, all terrestrial Monocotyledons — though the majority of the 

 orders of this class are still aquatic — show ancestral characters 



