6 THE BOOK OF NATURE STUDY 



by the fact that its spikelets contain only one perfect flower, 

 whilst the Sand-Lyme Grass usually has three perfect flowers in 

 I each spikelet. Both have leaves 



which can roll in, and thus protect 

 the plant from too rapid transpira- 

 tion. The structure of the leaf is 

 shown in Fig. 2. In wet weather, 

 or in diffuse light, the leaves are 

 spread out flat, but in scorching 

 suns and drying winds the upper 



FIG. 2.-Leaf of Psamma (transverse sur f ace rolls inwards, Owing to the 

 section). J, Position of stomata ; .. . . . .. 



m, motor cells; /, under surface; Contraction of Certain Cells. 



e, upper surface. The stomata are on the upper 



surface, and are completely sheltered by the inrolling of the 

 leaf. Very often with these two grasses, the Sand Sedge 

 (Carex arenaria) is also found ; it too has a creeping root- 

 stock and is a sand binder, but undoubtedly the most common 

 binder is the Marram Grass. Other plants soon find a lodg- 

 ment in the sand which is no longer being blown about ; the 

 Spiny Restharrow is often very conspicuous, carpeting the 

 ground to the very edge of the shifting belt ; mixed with this 

 may be found the Stork's Bill (Er odium cicutarium), a plant be- 

 longing to the Geraniaceae, but differing from the Geranium in 

 having pinnate, not palmate, leaves, and five instead of ten 

 stamens. The long beaks of the fruit are very characteristic ; 

 they twist themselves spirally, but the carpels do not open to let 

 out the seeds, as in the Geraniums. A geranium that is very 

 abundant on this part of the Northumberland coast is the Blood 

 Geranium ; this has large, purplish-red flowers, which are very 

 striking on the sand mounds and hills against the brownish grass. 

 This is a very local plant, but is usually abundant when it occurs 

 at all. The well known Bird's-foot Trefoil and the Mallow are 

 also common. One more plant must be mentioned as characteristic 

 of this situation, the Sea Purslane (Arenaria peploides), which 

 also has a creeping root-stock and is a sand binder. The leaves 

 are thick and fleshy, and the fruits are large compared with those 

 of other species of Sandwort. 



The Plant associations to be studied on sandy seashores are : 



