194 



OXYLOPHYTES SECT, vi 



5. Sclerophylly is frequent and is due to thickness of the epidermal 

 wall, as in Andromeda polifolia, Vaccinium Oxycoccos, V. Vitis-Idaea, 

 and Ledum palustre, and is perhaps correlated with the perennial 

 character of the leaves concerned. 1 



6. Mucilage occurs, for instance, in the epidermal cells of Berchemia 

 scandens 2 ; and a continuous hypoderma is present beneath the epidermis 

 on the upper leaf-face of Pieris nitida. 



7. Ericoid leaves. Many moor-plants have flat broad leaves ; but 

 some species possess ericoid or filiform leaves whose stomata are enclosed 

 in secluded spaces, so that water- vapour escapes with difficulty such 

 is the case in Erica Tetralix, Empetrum, Calluna vulgaris, and other 

 species to be mentioned in the next group. 



8. Terete leaves, aphyllous stems. The assimilatory organs of many 

 moor-plants and marsh-plants assume the form of erect, terete leaves or 

 aphyllous stems, as in Equisetum limosum, species of Junci genuini, 

 and other species of Juncus to a less extent, Scirpus palustris, S. caespi- 

 tosus, S. (Heleocharis) lacustris, and other species, Eriophorum vaginatum, 

 Carex microglochin, C. dioica, C. chordorrhiza, and C. pauciflora. 



9. Bilateral leaves. Leaves exposing their edges (profile-he) are met 

 with in Iris, Narthecium, Acorus, and Xyris. The leaves are flat, broad, 

 but likewise erect or upwardly directed, long, and undivided, in Alisma 

 Plantago, Sagittaria, and other Alismaceae, Butomus, Typha, Sparganium, 

 Ranunculus Lingua, and Lathyrus Nissolia. 



10. Closure of leaves. Broad-leaved Cyperaceae can close their leaves 

 together (always ?), and distinctly so in Carex Goodenowii ; yet the 

 stomata are not confined to the upper face. 



This xeromorphy of plants growing on wet moor-soil occurs all the 

 world over ; it is known not only in Europe, 3 but also in America 4 and 

 New Zealand. 5 



It is evident that there must be a causal connexion between the 

 soil and the xeromorphic structure which has been described, but it 

 would never be anticipated. The soil must be physiologically dry. In 

 genera which include not only paludal species, but also mesophytic 

 species not growing in dry places, we frequently find that the latter 

 have the broadest leaves, although the contrary might be expected. 

 The paludal Epilobium palustre and Lysimachia thyrsiflpra are the 

 narrowest-leaved species of their genera in our country ; Galium palustre 

 and G. elongatum likewise have narrower leaves than the mesophilous 

 species possess ; and other cases might be cited. 



Here attention may be directed to the remarkable fact that many 

 species of heather-plants can grow both on extremely dry, warm soil, 

 and on extremely cold, wet soil ; such is the case with Calluna, Empetrum, 

 several species of Pinus, Juniperus communis, Betula nana, Saxifraga 

 Hirculus, Ledum palustre, and Vaccinium Myrtillus in Europe, 6 Pinus 

 Taeda in the Dismal Swamps of the United States, 2 and Phormium tenax 

 in New Zealand. 7 One would, therefore, assume that between the two 



1 For anatomy see H. E. Petersen, 1908. * Kearney, 1901. 



3 Volkens, 1890; Kihlman, 1890; Raunkiar, 1895-9,1901 ; concerning the British 

 Isles, see Miall, 1898 ; Rob. Smith, 1899. 



4 Kearney, 1901 ; Pound and Clements, 1900. * Cockayne, 1901, 1904, 19050. 

 * See Grabner, 1895, 1901. 7 Cockayne, 1904. 



