76 MISSOURI BOTANICAL GARDEN. 



occurrence of tannin and a bitter principle in others ; their 

 protandry and exclusive adaptation to wind pollination (c/. 

 Miiller's writings, and notes by Thomson in Trans. Bot. Soc. 

 Edinburgh, xiv. 105, and Tulberg in Bot. Notiser, 1868, 

 12) ; and the adaptation of the greater number of species 

 to wind dissemination, by the enlargement of the inner seg- 

 ments of the perianth during ripening, although some of 

 those with fimbriate valves may profit by attachment to 

 animals, while R. Lappula and R. hamatus form verita- 

 ble burs, as Huth has shown in Bibl. Bot. 1887, No. 9, p. 

 13 (Just, xv. part 1,433). Causation of sex in the dioe- 

 cious R. Acelosella is discussed by Hoffmann in Bot. Zeitung, 

 xliii. Chatin describes the organogeny of the androecium 

 in Comptes Eend. vol. 78, 254 (Just, 1874, 479). Heraii 

 considers the anatomy of the stem, in Ann. des Sci. Nat. 7 

 ser. ii. 283 and 286; and Hanstein describes the mucilage 

 glands of the buds in some cases in Bot. Zeit. 1868, 699 

 and 799. The occurrence of tannin in considerable 

 quantities is considered by Bandelier in Verhandl. Ge- 

 sellsch. f . Erdkunde zu Berlin, 1885, xii (Just, xiii. part 2, 

 234) ; and Borscow notes the presence of chrysophanic 

 acid in the roots, in Bot. Zeit. 1874 (Just, ii, 126, 834). 

 Other references concerning economic products and prop- 

 erties in the genus, few species of which are of any con- 

 siderable economic importance, are given under the 

 several species, particularly R. hymenosepalus , and the 

 copious indexes of such pharmaceutical periodicals as the 

 American Journal of Pharmacy. 



SYNOPSIS OF NORTH AMERICAN SPECIES. 



Acetosella. Dioecious inner segments of perianth without dorsal 

 callosity, not reticulated, not larger than theachene: foliage acid. 

 Perennial. 



1. R. ACETOSELLA, L. A span to exceptionally a foot or 

 two high, tufted, propagating by creeping roots; leaves 

 rarely 5 cm. long, oblanceolate, acute, the lower mostly 



