114 Chase — Notes on Genera of Panirea'. IV. 



rachis at an angle of about 45 degrees), alternate spikelets placed with 

 the back and alternate spikelets placed with the face toward the rachis 

 (that is, the first glume alternately introrse and extrorse), a short callus 

 below the spikelet ; first glume minute, often hyaline and nerveless ; second 

 glume membranaceous, shorter than the spikelet; sterile lemma subin- 

 durated, thinner down the middle and early splitting to the base (the 

 margins of the split rolling inward ) or deeply sulcate only, the sterile 

 palea nearly as long as its lemma, the nerves and margins firm, the broad 

 internerve very thin, a staminate flower present or wanting ; fruit 

 oblong-elliptic, subacute, the lemma and palea cartilaginous-indurated, 

 papillose, the summit of the lemma often clothed with stiff hairs, the thin 

 margins flat, more or less pubescent. Slender, branching perennials, 

 with narrow leaves, the genus confined to the tropics of the mainland of 

 the western hemisphere. 



The strictly racemose inflorescence, the alternation in the position of 

 the spikelets, the subindurated, split or deeply sulcate sterile lemma, and 

 the cartilaginous ( not chartaceous ) indurated lemma and palea, the thin 

 margins of the lemma flat, taken in combination, are here used to distin- 

 guish Thrasya from Panicum and Paspalum. Thrasya approaches Pas- 

 palum through Thrasya cultrata and Panicum campylostachyum ( in 

 which the fruit is not hairy at the summit) on the one side and Paspalum 

 ■monostachyum (H. B. K.) Vasey (in which the slightly indurated sterile 

 lemma is somewhat sulcate and readily splits in dissection, and the firm 

 margins of the papillose fertile lemma are not inrolled), on the other side. 

 In the latter species, however, the paired spikelets are in two rows, and 

 not in the alternately reversed position of those of Thrasya. If we con- 

 ceive of a genus as bounded by an orbiculate line in places farther from, 

 in places nearer to, the center (the species conceived to be the type of the 

 genus) we have Paspalum monostachyum close to the line in one circle and 

 Panicum, campylostachyum and Thrasya cultrata close to the line in the 

 adjoining one, the theoretical common ancestor of both long extinct. In 

 such cases of extra-generic affinity it seems to be the nearest approach to a 

 natural arrangement if we place the anomalous species in the genus 

 to the members of which it is on the whole most nearly allied. And 

 Paspalum monostachyum finds its nearest allies in Panicum unispicatum 

 Scribn. & Merr. and a few other species of the section Harpostachys or 

 Dimorphostachys of Paspalum. 



The following species belong to this genus: 



Thrasya paspaloides H. B. K. Nov. Gen. & Sp. 1 : 121. pi. 39. 1816. 

 (See above. ) 

 Panicum thrasya Trin. Mem. Acad. St. Petersb. VI. Sci. Nat. 3 : 2 228. 

 1834. Based on T. paspaloides H. B. K. Only the Humboldt and Bon- 

 pland specimen is mentioned. It is possible that this species has not been 

 collected a second time. 



Thrasya thrasyoides (Trin.). 



Panicum thrasyoides Trin. Gram. Pan. 126. 1826. "Brasil. (Langs- 

 dorff)." The type specimen, in the Trinius Herbarium, is labeled 



