Mr. Woops on the Genera of European Grasses. 11 
closely on Trisetum among the Avenacee, yet I think the line of division is cor- 
rectly drawn. On the other hand, Brachypodium and some other plants render 
very faint and obscure the separation of the Festucaceæ and Hordeaceæ. 
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 is uniformly glumaceous, a term 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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