biseriate.

Spikelets villous. 1. P. Isachne.

Spikelets glabrous.

Spikes shorter than the internodes. 2. P. flavidum.

Spikes longer than the internodes. 3. P. fluitans.

(b) Spikelets 3- to 5-seriate.

Third glume awned.

Stems stout, erect. 4. P. Crus-galli.

Stems stout, prostrate at base. 5. P. stagninum.

Third glume cuspidate.

Stems slender. 6. P. colonum.

II. Rachis of spikes narrow, filiform,
terete or angular.

First glume shorter than the third.

First glume semilunate, about 1/4
of the third glume. 7. P. prostratum.

First glume 1/2 of or less than
1/2 of third glume, 5-nerved. 8. P. ramosum.

Leaf base broad or cordate.

Fourth glume shortly awned. 9. P. javanicum.

Fourth glume muticous. 10. P. distachyum.

B. Inflorescence a contracted or open panicle.

I. Panicle contracted and spike-like.

Spikelets lanceolate and first glume
minute. 11. P. interruptum.

II. Panicle effuse.

Annuals; first glume nearly 3/4 of
the third glume. 12. P. trypheron.

Perennials; first glume less than
1/3 of the third glume. 13. P. repens.

[Illustration: Fig. 80.--Panicum Isachne.]

=Panicum Isachne, _Roth._=

This is an annual grass usually growing in tufts with fine fibrous roots
and many slender spreading branches, all of them at first creeping and
horizontal, rooting at the nodes and then becoming erect and varying in
length from 1 to 2 feet.

Stems are very slender, glabrous or covered with scattered hairs,
purplish or pale green, and branching freely towards the base.

The _leaf-sheath_ is shorter than the internodes, green or purplish,
striate, externally hairy with scattered bulbous-based hairs, varying in
length from 1/2 to 3 inches, the outer margin of the sheath is ciliate
with long hairs and at the mouths sometimes long hairs are present,
especially when the leaves are young. The _ligule_ is merely a dense
fringe of long hairs. _Nodes_ are tumid, purplish, covered with long
hairs.

The _leaf-blade_ is flat but convolute when young, lanceolat