ON THE EUROPEAN SPECIES OF FESTUCA. 279 



than those drawn from the leaves of the culm. The former live 

 for six months, and have to accommodate themselves to very varied 

 conditions ; the latter live ahout one month only, for they die soon 

 after the flowers are perfected. 



Out of twenty-eight species of Festuca described by Prof. Hackel 

 there are eighteen with split sheaths, eight with closed sheaths, 

 one in which the character of the sheath is variable [F. ovina), and 

 one in which the character of the sheath has not been observed, 

 viz., F. Morisiana. The sheath of the uppermost leaf of the 

 innovation should be chosen for examination. 



The closed sheaths of F. scaherrima and amethystina are very 

 remarkable. The upper half of the sheath is split, the lower half 

 is closed, though the tw^o edges overlap, the connection being 

 effected by a membrane which lies behind a deep and narrow 

 furrow. The closed sheaths of other species are even and un- 

 furrowed. Hence the above character is a most valuable one. 



Valuable characters may be drawn from the marcescent sheaths. 

 Some become filamentous, while others have a thick and im- 

 perishable epidermis, so that the fibres do not become freed. Very 

 remarkable is the way in which the slieath withers in two Spanish 

 si3ecies, F. Clementei and F. plicata ; the sheath becomes trans- 

 versely rugose or striped, and ultimately transversely filamentous ; 

 this is better seen in the former than in the latter species. 



Koch uses the character taken from the ligule to mark not only 

 species, but sections ; but although of great value, it cannot be 

 satisfactorily thus used. Dutailly, in 1878, pointed out that 

 F. eskia, Eam., is furnished with three delicate nerves. 



The vernation of Festuca is usually conduplicate when the blade 

 continues to bear the same form which it had when in the bud ; it 

 is therefore wrong to describe the leaves of F. ovina and F. varia 

 as convolute ; they are oftener complicate. 



The flattening out of the leaves of Festuca, as of all grasses, is 

 caused by the turgescence of cells which lie betw^een the ribs on 

 the upper side of the leaf ; and the cells between the ribs near the 

 centre of the leaf swell more than those near the side. Prof. 

 Hackel adopts Duval Jouve's name, cellulfB bulliformes, for these 

 cells ; and as they are universally present in flat leaves, their 

 presence may be ascertained, even if the leaf be dry, rolled up, and 

 withered, and the character of the leaf determined, whether, when 

 living, it was flat or otherwise. Nevertheless too great dependence 

 should not be placed on this character, as the cells, though present, 

 are sometimes hardly larger than the surrounding ones. In damp 

 weather and in wet situations, true folded leaves, in which no 

 cellul^e bulliformes are present, may unfold and present the 

 appearance of flat leaves. Excellent magnified representations of 

 sections of the different forms of the leaves ai'e given in three 

 plates. The comparative width of the blade is of great value as a 

 distinctive character in determining species, subspecies, and 

 varieties, but only in the case of those which have folded leaves ; 

 it is valueless for those which have flat leaves. 



The form of the extremity of the leaf affords important 



