FLORA OF THE EAST RIDING OF YORKSHIRE. 1 79 



141 5. Populus nigra. Linn. 

 (Black Poplar). 

 Alien. 



Large Tree. Frequent near Hull, as on Cottingham 

 Lane. 



CERATOPHYLLE^. 



1417. Ceratophyllum demersum. Linn. (?). 



(Common Hornwort). 



Native, Eng., i, 2, 6. June, IV. 



Market Weighton Canal and Hornsea Mere (Y.N.U.). 

 Arram Beck (1898). River Hull at Wansford.* Ponds at 

 Marfleet, near Hull (C.W.).* 



CONIFER.E. 



142 1. Taxus baccata. Linn., 52. 



Native, Eng., 1-7. March, III. 



Frequent, but always in cultivated places, and I think it 

 is never truly wild in the East Riding. 



1422. Pinus sylvestris. Linn., 17. 



(Scotch Fir). 



Native, Scot., i, 2, 6, 7. May, IV. 



Frequent, and in many cases only a denizen ; but on 

 Skipwith Common it is native (W.N.C.). The stumps are 

 often met with in post-glacial "forest beds," as at Chalk 

 Lane brickpond within the borough of Hull.* 



HYDROCHARIDE^. 



1424. Elodea canadensis. Michx. 



(Water Thyme, Canadian Pond weed). 



Denizen, Atlantic. August. 



Common in the dykes and drains, but scarcely so con- 

 spicuous as it was a dozen years ago. 



