Bluets whiten the fields, and violets are now perhaps in prime.

May 21. 

P. M. —To Island. 

Salix nigra leafs. 

Is that plump blue-backed, rufous rumped swallow the cliff swallow, flying with barn swallows, etc., over the river? Nuttall apparently so describes it. It dashes within a foot of me. 

Lambkill leaf, a day or two. Choke-berry pollen; perhaps a day or more elsewhere. Viola palmata pretty common, apparently two or three days. Some button bush begins to leaf. Cranberry well started; shoots three quarters of an inch. 

dog-tooth violet
May 21, 2017

Bluets whiten the fields, and violets are now perhaps in prime. 

Very cold to-day; cold weather, indeed, from the 20th to 23d inclusive. Sit by fires, and sometimes wear a greatcoat and expect frosts.

H. D. Thoreau, Journal, May 21, 1855

Bluets whiten the fields, and violets are now perhaps in prime. See May 7,1860 ("I saw bluets whitening the fields yesterday a quarter of a mile off. They are to the sere brown grass what the shad-bush is now to the brown and bare sprout lands.")
Very cold to-day; cold weather, indeed . . . See May 21, 1860 (“Cold, at 11 A.M. 50°; and sit by a fire”)