Sentence:  I have more than once sat cross-legged in the grass through a long summer morning and watched without touching while a poppy bud higher than my head slowly but visibly pushed off its <WSD>cap</WSD> , unfolded , and shook out like a banner in the sun its flaming vermilion petals . 
Meaning of the word marked with <WSD> tags:  something serving as a cover or protection