Mr. Woods on the Genera of European Grasses. 11 



closely on Trisefum among the Avenacece, yet I think the line of division is cor- 

 rectly diaM'n. On the other hand, Brachypodium and some other plants render 

 very faint and obscure the separation of the Festucaceœ and Hordeaceœ. 



In considering what forms a group of genera, it is necessary to determine 

 those points in their structure in which all, or the greater part of them agree, 

 in order that we may not depend for distinction on marks which run through 

 a great many groups. This seems sufficiently obvious in all classification ; 

 yet probably every botanist would be able to produce examples where genera 

 have been founded, or species formed, on characters which are common to 

 numbers. We determine a plant to be a Grass, by its knotted culm, each knot 

 giving rise to a striate sheath, which terminates in a leaf of similar texture. 

 These leaves are generally narrow; but as there are plants with broadish leaves, 

 i. e. the breadth of which is as much as half their length, which every botanist 

 would without hesitation pronounce to be Grasses, it appears that this circum- 

 stance is not essential to our notion of a Grass. Another essential particular is 

 in the flower, which isuniformly li/wwiaceoe/^, aterm which on the present occa- 

 sion it cannot be necessary to explain. Without a structure of this sort a plant 

 would not be a Grass, nor would it be esteemed such unless it had a single 

 monocotyledonous superior seed not inclosed in a capsule or pericarp. 



These circumstances being common to all Grasses cannot be made use of 

 in distinguishing genera, or the tribes into which we may incline to distribute 

 the genera ; but there are various particulars in the inflorescence and in the 

 distribution and structure of the glumes and palea, and in the organs of repro- 

 duction to which we can refer for this object. The inflorescence is in most 

 cases reputed to be too uncertain in its nature to form a good foundation for 

 the establishment of genera; but in Grasses, where the genera are, perhaps, 

 formed in many cases for the convenience of the student, rather than because 

 nature has established any marked difference between them, I know of no 

 botanist who has been able to do without it. Even the pubescence of certain 

 parts, a character in general of little value even in the determination of spe- 

 cies, has been universally admitted as part of the character of a genus. If in 

 these cases we must take care not to push the license too far, nor to conclude, 

 because a peculiarity in some plants coincides with other circumstances, so as 

 to form a valuable groundwork for the separation of genera, that it must do 



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