Grasses 
Fic. 40.—Oats and yarrow. 
a, A cluster or “spikelet'’ of oat-blossoms; 4, a cluster or “head” of yarrow- 
blossoms ; c, a single oat-blossom with its enfolding ‘“‘glumes”; d@, a single 
yarrow-blossom with its attendant ‘‘ bracteole.”” 
