of these species belong toPoaccte, and fifteen to Pankete. This relative proportion of-these two tribes is considerably different from what might have been expected, in the climates in which the collection was formed: it, seems, however, to be connected with the. nature of the surface, for in the Great Desert the reduction of Panicese is still more remarkable; this tribe being to Peace®, in that, region, in the proportion of only five to eighteen. Dr. Oudney remarks with respect to the grasses of the ■ desert, that he observed no species with creeping roots; for a species of Arundo related to Phragmites, which he notices as the only exception, is not properly a desert plant. Among tire, very few Graminese deserving particular notice, the first is A v b n a P o r s k a i . i i of Vahl, The specimens in the herbarium which were collected in the desert of Tintuma in some respects differ from all the others that I have seen of this variable species. In the,, Banksian herbarium there is an authentic specimen from Forskal ; I have received from M. Delile specimens both of his A. Forskalii and arundinacea, desoribedand figured in his Flore d’Egypte ; and am also in possession of others in somewhat different states, collected in Egypt by M. Nectoux and Dr. Sieber. Prom a comparison of all these specimens, I am led to believe, that A, Forskalii and arundinacea are not specifically distinct; and it is at least evident, that arundinacea more nearly approaches to the plant of Forskal than that to which M. Delile has applied the, name Forskalii. This grass, which does not belong to Avena, is referrible to Danthonia, f r o m the structure of the outer, valve of,its perianthium. But Danthonia requires subdivision into several sections, of which, perhaps, our plant may be considered as, forming one. The character o f the section established on Danthonia Forskalii would chiefly consist in the very remarkable obliquity of the joints of the locusta, which is, indeed, so great, that after their separation each flower seems to have at the base an almost vertically deseendent spur ; and as the inferior extremity of the upper joint is produced beyond the lower, a short calcar actually exists before separation, and this calcar is equally manifest in the terminal rudiment of the locusta. The present, therefore, is a case of more remarkably oblique articulation in grasses than even that existing in Holcus acicularis (Andropogon acicularis, Retz), which led to the formation of Cmti-opkoinbh ■; a gemra'Still admitted by Professor Sprengel*, and respecting the Structure o f which a very singular explanation has1 been lately offered by M; Raspailfi In one respect, the two cases differ.' In Danthonia (Centropodia) Forskalii, the articulations being in the axis of the'locusta Or spicula,' eakflt flower appears1 tb have this spur-like process; while in Holcus (Rhaphls) acicularis, the joint being in the peduncle1 'Or branch of the racemus, the spur is common-to three locust®. Dr. Fischer, in whose herbarium the specimen was observed which , led t'o the formation of Centrophorum, will probably recollect the communication made to him on the subject of that plant, of which Dr. Trinjos himself has since corrected the characters. He retains it, however, as a distinct genus; fbr which he has adopted the name Rhaphis, given to it by Loureiro, by whom it was originally proposed, on other, but not more satisfactory grounds. I' T r jb r a p h i s F u m i l t o is the second plant of this family to be noticed, It'.'is undescribed, and belongs to a genus of which the only two published species were found in the intratropical part of New Holland!. In several points of structure the African plant is very different from T. pungens, the first of these species ; in some respects it approaches to mollis, the second species; especially in the inequality of its setae or aristae, but it differs from both inhabit, and'in having only one perfect flower in each locusta §. O f P e n n i s e t u m d i c h o t o m u m , (Delile, Flore d’Egypte, p. 15,: tab. 8, f. IBf which, in several different states, is in the collection, it is remarked by Dr. Oudney, that “ it is a great annoyance to man and beast,''from th e 1 prickly calyx (involuorum) and by Major Denham, that 'from Aghedem, to Woodie “ it covered the surface of the country, and annoy ed' the travellers to misery he observes, also, that the seed-is called Kashdia, and ¡is1 ^eatehl * Syst. Veg. 1. p. 132. t Annal. des Scien. Nat. 4. p. 425. j Prodr. Flor. Nov. Holl. 1. p. i85. § Triraphis Puniilio, panicula coarctata abbreviata/locusta glurriam vix supcrante 3-4- flora : flosculo infimo hermaphrodite; reliquis neutris univalvibus.
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