CHAP. Lxx DRY SAND-FIELD 267 



point at the upper end of the primary root ; such is the case with Artemisia 

 campestris and Ononis. 



(c) A few possess epigeous creeping shoots : among such are Antennaria 

 dioica, Hieracium Pilosella, Polypodium vulgare, and in most cases 

 vSedum acre. 



[d) Annual {ephemeral) and biennial {hibernating annual) species are 

 common, showing that the dune largely partakes of the nature of steppe. 

 The latter species germinate in autumn or spring, develop, and flower 

 in early spring, but conclude their lives before the onset of the summer's 

 heat. It is the warm soil that occasions this acceleration of development, 

 which is exhibited by Cerastium semidecandrum and C. tetrandrum, 

 TrifoUum arvense, Filago minima, Aira praecox, Bromus mollis, and 

 Phleum arenarium, as well as by Jasione montana, Draba vema, and 

 Tecsdalea nudicaulis. To these types we may append Eryngium mari- 

 timum which is, at least often, perennial but is reputed to be monocarpic. 

 This abundance of small, annual, rapidly-flowering plants is in accord 

 with the prevailing dryness, intense insolation, and sterility of the soil. 

 But we have further to note that : 



The perennial herbs, grasses, and shrubs as a whole, are low, small- 

 leaved, and narrow-leaved. 



Most of the grasses, including Psamma, Triticum junceum, Nardus, 

 Festuca ovina, F. rubra f. arenaria, Koeleria glauca, have deeply fur- 

 rowed leaves that can close themselves more or less by rolling up ; not a 

 single grass possesses broad, lush, bright-green leaves. 



Elymus arenarius has broad leaves which, however, are blue-green 

 with wax, like those of Triticum junceum. Wax coats the leaves of 

 Lathyrus maritimus, Eryngium maritimum, Mertensia maritima, Glaucium 

 flavum, and Crambe maritima. 



Woolly hairs clothe Salix repens, Gnaphalium, and Antennaria. 



Hippophae has scaly hairs. 



Glandular hairs are developed on Senecio viscosus. Ononis repens, 

 Cerastium semidecandrum, and some other plants, to such an extent that 

 the surface of the plant is densely coated with sand. 



Nardus and Koeleria glauca are tunic-grasses. 



Not a few species depress their transpiration by having the leaves 

 vertical, as in Salix repens, or crumpled, as in Eryngium. 



The leaves of certain psammophytes are dorsiventral in structure and, 

 although their blades are horizontal, they have palisade parenchyma 

 on the lower side : according to Vesque ^ and Giltay - this must be 

 attributed to the intense hght reflected from the sand. 



Thorny structures occur in Hippophae, thus rendering its buslics 

 almost impenetrable, also in Eryngium and Ononis. 



The leaves of many plants present are closely applied to the soil, 

 and many species spread all their shoots horizontally over the sand, 

 presumably because of the prevailing thermal conditions.^ 



Succulent plants are represented only by a few species including 

 Sedum acre. 



As a means of defence against the mechanical action of wind, the 

 sea-marram has a power of turning its leaves in an arched fashion with 



' Vesque, 1882. ^ Giltay, 1886. Seep. 26. 



