'AS Mr. H^ooDS on the Genera of European Grasses. 



are only 2, not uiiich alike in general appearance, ^/. globosa and ^/. agro- 

 stidea, and of these he calls the first " species anomala," and doubts if it do 

 not rather belong to Aira: yet this is, I believe, the original species. In 

 A.globusa the outer palea is rather firmer than the glume; in J. agrostideu 

 the palea? are the thinnest and most pellucid. A. agrostidea has perfectly 

 smooth paleoe, contrary to the generic character of Airopsis. In most of the 

 Amv the seed seems to be loose and the corolla unchanged ; but in A. cari/o- 

 j)/ii/IIea, prœcox, capillaris, pulclieUa, and probably some others, the paleœ 

 harden upon the seed. Tiiese are very different in habit from A.Jiexuosa, 

 and I have doubted whether it might not serve as a foundation for remodelling 

 the genera, but I have not materials for following out the investigation. The 

 outer ])alea is without any prominent nerve or rib in the hitherto acknow- 

 ledged species ; but I have a small Grass from the neighbourhood of Rome, 

 which in many respects is an Aira, and with the habit of ^îlra can/op/ri///ea, 

 where the outer palea is strongly ribbed, much firmer than the glume, and fully 

 as long, but it does not harden on the seed. I propose to call it Aira costata ; 

 paled inferiore cost aid glumisjirmiore immutatd. 



The single flowers of Lagurus separate it from the rest of the tribe, and the 

 compact head might lead the student to place it among the Plileineœ, Ijut an 

 examination of the florets will certainly induce him to seek for it licre. 



Of Trisetum Kunth says, "Differt ab .lira non nisi numéro florum ;" but 

 T. /dileoides, T. molle, T. toluccense, T. elongafam, T. condensatam, T. hvflingi- 

 anum, T. Cavanillesii are descnl>ed by himself as having only two flowers. 

 Why do they not belong to Aira ? I am more disposed to rest the difilerence 

 on the comparative length of the glumes, which in most species of Aira con- 

 siderably exceed the spicula. Yet this is not the case in A.Jiexuosa, which 

 perhaps might be joined to Trisetum. In iiabit the difference is more marked, 

 yet it is difficult to say precisely in what it consists. The panicle is more 

 dense in Trisetum than in most of the Airœ, yet, perhaps, not more than in 

 Aira prœcox, which nobody thinks of uniting with Trisetum ; perha])s we may 

 say that it chiefly depends on the crowded spiculee of the latter genus, while 

 those of Aira are very mucii scattered. To distinguish Trisetum from Arena, 

 we must, I think, depend chiefly on the seed, which in the former genus has 

 neither crest nor furrow. 



