180 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
Nodes, at least the lower, bearded. 
Spikelets 1.5 to 1.6 mm. long, glabrous (occasional in- 
dividuals with pubescent spikelets)...............- 102. P.microcarpon. 
Spikelets 2 mm. or more long. 
Spikelets glabrous, 2 mm. long; autumnal form top- 
heavy-reclining........--.----2++--+----2------ 110. P. barbulatum. 
Spikelets pubescent. 
Blades all velvety; autumnal form sparingly 
branched............-2-.------ cee ee eee 105. P. annulum. 
Blades glabrous, or only the lower pubescent or 
velvety; autumnal form freely branching. 
Spikelets 2 mm. long; autumnal form pro- 
fusely branching. 
Fruits slightly exposed at maturity; 
upper sheaths  viscid-spotted; 
autumnal form erect or reclining. .103. P. nitidum. 
Fruits covered at maturity; sheaths not 
viscid - spotted; autumnal form 
decumbent, with  flabellate - 
fascicled branches; Mexican..... 104. P. multirameum. 
Spikelets 2.2 mm. or more long; autumnal 
form less profusely branching. 
Sheaths and upper nodes glabrous......107.  P. clutei. 
Lower sheaths and all nodes pubescent..106. P. mattamuskeet- 
ense. 
Nodes not bearded. 
Spikelets pubescent. 
Culms erect, never becoming vine-like. 
Primary blades spreading; panicles purplish; 
fruit exposed at summit.................. 107. P. clutet. 
Primary blades erect; panicles green; fruit cov- 
ered (wood forms with spreading blades 
may be distinguished from P, dichotomum 
by pubescent spikelets, 2.2 mm. long)....108. J 
Culms soon prostrate, vine-like; branches divaricate. 
Plants bright green, culms lax; spikelets not 
over 2.1 mm. long....... ...114. JI 
Plants grayish green, culms. stiff; spikelets 2.5 
mm, long......... 2 ee eee eee eee eee ee eee 115. £ 
Spikelets glabrous. 
Culms soon prostrate. 
Plants bright green, culms lax; spikelets not 
over 2.1 mm. long......--.--.....-.------- 114. J 
Plants grayish green, culms stiff; spikelets 2.5 
mm, long....2......2. 2 eee ee ee eee ee 115. £ 
Culms erect, or the autumnal form topheavy, never 
prostrate. 
Spikelets not over 1.6 mm. long; panicles nar- 
row; plants glaucous bluish green........- 113. P. caerulescens. 
Spikelets 2 mm. or more long; panicles open. 
Blades erect, firm; spikelets turgid, strongly 
nerved; plants grayish olive green....112. P. roanokense. 
Blades spreading; spikelets not turgid. 
~ 
. boreale. 
~ 
. lucidum. 
~ 
. sphagnicola. 
- 
. lucidum. 
= 
. sphagnicola. 
