CLVII. GrRAMINEiE (Btapf). 
423 
sessile, digitate or more or less distant on a common axis, some- 
times bare at the base owing to the arrest of spikelets, rarely truly 
peduncled and panicled, simple or sometimes compound near the 
base ; rhachis triquetrous, lateral angles with narrow green margins 
or herbaceous wings or flattened with a terete midrib ; pedicels 
unequally long ; spikelets closely appressed and more or less imbricate 
or lax to veiy lax, usually silky though often apparently glabrous owing 
to the very tight application of the extremely fine hairs, rarely really 
glabrous . — Panicum § Digitaria, Benth. et Hook. f. Gen. PI. iii. 1101. 
Species over 100, in the warm parts of both hemispheres, most numerous in 
the Old World. 
Haller (H^. Stirp. ii. 244, 1768) was the first to give a full and correct descrip- 
tion of the genus as here understood and is therefore accepted as its author. 
The usual quotation “ Digitaria, Heist, ex Adanson ” (Fam. PI. ii. 38 ; 1763) is 
inadmissible in this place, as Adanson meant by it Tripsacum, L., whatever 
Heister’s notion of Digitaria may have been. Scopoli (FI. Cam. i. 52 : 1772) 
and Wiggers (Prim. FI. Hols. 6 : 1780) took the genus from Haller ; Wiggers 
adding a short differential diagnosis. Syntherisma, Walt., established in 
1788, rests on an American species of Digitaria. 
The nature of the hairs of the spikelets is remarkably varied and the several 
types of hairs which can be distinguished are so correlated with other characters 
suggesting close affinity that they may be treated as reliable guides to the 
main groups of species. Unfortunately the hairs are frequently so delicate 
(a very few micromillimeters in diameter) that a compound microscope is 
required to see the details of their structure. It has therefore been considered 
desirable in drawing up the key to support them as far as possible by less micro- 
scopic characters, although they may not always be of the same precision or 
constancy. Where the hairs are very fine and at the same time closely appressed 
to the valve they may become practically invisible even with the use of an 
ordinary lens. They can, however, always be detected if the spikelet is soaked 
and the surface rubbed with a needle from the tip downwards, or if examined 
under a higher power. The nervation of the upper glume and barren valve, 
another character of technical importance, is frequently obscured by the in- 
dumentum, but can generally be seen sufficiently clearly on the inner glabrous 
face of those organs after they have been flattened out in a drop of water. The 
all but constant presence of a very much reduced dorsally papillose valvule 
and of apparently functioning lodicules in the barren floret is a very interesting 
fact and a good generic character, but the parts are too minute and too similar 
to afford a practical means for specific discrimination. The valve and valvule 
of the upper floret are so similar in consistency and colouring that no attempt 
has been made to describe them separately, and the corresponding characters 
attributed to the floret are meant to cover both. 
Here and in all the genera of Panicastra where the terms “ spikelets abaxial ” 
and “ spikelets adaxial” are used, “abaxial” signifies that the face of the 
spikelet with the lower glume at the base and the valve of the upper floret 
(glumes i. and iii. of authors) above it are turned a^ay from the rhachis, while 
“ adaxial” means that the fane of the spikelet faces the rhachis. Applied to 
the back of the fruit (see key to genera, p. 14), the terms have, of course, to be 
reversed; the back of the fruit of an adaxial spikelet is abaxial, and the 
back of an abaxial spikelet is adaxial. 
Key to the Sections and Subsections. 
*Spikelets mostly hairy, although frequently apparently 
glabrous, not accompanied by white setulse of equal 
or greater length ; barren valve 7-, or more rarely 
5-nerved 
I. Eu-Digitaria. 
