Ord. 7.] DIOECIA ENNEANDKIA. 205 



DIOECIA OCTANDRIA. 



456. PoPULUS. Poplar. 



1. P. alba, 23. 1618. (White P., Abele Tree.) Leaves lobed and 



toothed ; somewhat heart-shaped at the base ; snow-white and 

 densely downy beneath. Fertile catkins ovate. Stigmas four. 

 Moist woods. T? . 3. Tree, with smoothish bark, and horizont. br. 

 Wood white. 



2. P. canescens, 23. 1619. (Grey P.) Leaves roundish, deeply waved, 



toothed ; hoary and downy beneath. Fertile catkins cylindrical. 

 Stigmas eight. 

 Turfy mead. Tj . 3. A tall tree, with more upright br. Bark silvery. 

 Wood valuable. 



3. P. tremula, 27. 1909. (Aspen, or Trembling P.) Leaves nearly 



orbicular, toothed ; smooth on both sides. Footstalks compressed. 



Young branches hairy. Stigmas four, erect, auricled at the base. 



Moist woods. \i . 3, 4. A lofty round-headed tree. L. quivering. 



4. P. nigra, 27. 1910. (Black P.) Leaves deltoid, pointed, serrated, 



smooth on both sides. Catkins all lax and cylindrical. Stigmas 

 four, simple, spreading. 

 Watery pi. \ . 3. A tall tree. Bark thick, blackish. 



457. RHODl'OLA. Rose-root. 



1. R. rosea, 8. 508. (Mountain Rose-root.) 



Fiss. of alpine and northern maritime rocks. If. 5, 6. Leafy, a 

 span. L. obov. fleshy. Cyme of yellow Ji. 



DIOECIA ENNEANDRIA. 



458. MERCURliLIS. Mercury. 



1. M. perennis, 26. 1872. (Perennial M.) Stem perfectly simple. 



Leaves rough. Root creeping. 

 Banks. If. 4, 5. Herb, rough, fetid, poisonous, If. L. ovate. Fl.gr. 



2. M. annua, 8. 559. (Annual M.) Stem cross-branching. Leaves 



smooth. Root fibrous. Barren flowers in numerous, spiked, al- 

 ternate tufts. 

 Waste and cult. gr. 0. 7 — 9. A bushy, bright green herb, 6 — 12 in. 



459. HYDR6CHARIS. Frog-bit. 



1. H. Morsus rana, 12. 808. (Common Frog-bit.) 



Ditches and ponds. If. 7. A floating, smooth herb, increasing by 

 runners. L. entire, not 2 in. broad. Fl. nurner. white. 



