8o 
Colorado Agricultural College 
2. Blue Lettuce (Lactuca 
pulchella {Pursh.) DC.) (Fig. 
157). — Seeds deep mouse-gray in 
color, mostly 3-veined, slightly mar- 
gined, flattened, mottled, rough 
throughout, 2.5-3 mm. long, .6-1 mm. 
wide, gradually tapering into a 
short beak ; seeds less hairy than 
L. scariola but otherwise the same 
except in color. 
Fig-. 157. Blue 
Lettuce (Lactuca 
pulchella). x 15. 
3. Sow Thistle 
(Sonchus (Tourn.) L.) 
Achenes flattened, 10-20 ribbed, marked with blunt projections through- 
out, even or square at the apex as though cut off transversely ; pappus of 
tine bristles mostly falling off together. 
Key to Soeciess 
Seeds distinctly flattened 
Seeds roughened transversely 1..8. oleraceus 
Seeds not roughened, mostly 3-ribbed on each side 2..S. asjier 
Seeds only .slightly flattened, 6-8 ribbed on each side ; roughened 
transversely 3..,Sf. arvensis 
1. Annual Sow Thistle, Common Sow Thistle 
{^onchus oleraceus L.) (Fig. 15S.— Seeds russet in 
color, flattened, slightly roughened transversely, 
5-ribbed (one central rib and two on each side of the 
central rib parallel to it but close together giving a 
groove-like appearance on each side, thus 5-ribbed and 
2-grooved), slightly margined, 2.5-3 mm. long, .7-1 mm. 
wide, in the widest part, narrowed at the base. 
Fig. 158. An- 
nual Sow-Thistle 
(Sonchus oler- 
aceus). X 12. 
2. Spiny-leaved, Spiny, or S h a r p- 
FRiNGED Sow Thistle (Sonckus usper (L.) 
All.) (Fig. 159). — Seeds russet in color, 
flattened, smooth, mostly 3-ribbed on each 
side, distinctly margined, blunt, thin, 2.5-3 
inm. long, 1.2-1 .4 mm. wide in the widest 
part, distinctly wider than S. oleraceus or 
S. arvc7isls. 
Fig. 159. Spiny- 
leaved Sow- 
Thistle (Sonchus 
asper). x 12. 
