ELODEA 465 



part of the district from Wokingham to Blackwater, and from 



Wokingham to Windsor Park and Bagshot. 

 P. sylvestris occurs under similar conditions in Surrey and Hampshire. 

 A large number of planted Conifers are to be seen in the county, 

 sometimes in a semi-wild condition. 



MONOCOTYLEDONES, Juss. Gen. 21 (1789). 



VALLISNERIACEAE, Dumort. Anal. Earn. 54 (1829). 

 Hydrocharidaceae, Lindl. Veg. King. 141 (1847). 



ELODEA, [Rich, in] Michaux, Fl. Bor. Amer. i. 20 (1803). 



*Elodea canadensis, Mich. I.e. Canadian Thyme, American Water Weed, 

 Water Thyme. 



Udora canadensis, Nuttall, Gen. N. A. PI. ii. 242 (18 18). Anacharis 

 Alsinastrum, Bab. in Ann. Nat. Hist. Ser. ii. (1848) 83. Philotria 

 canadensis, Britton, in Science, (ii) ii. (1895) 5. 



Comp. Cyb. Br. 582. Syme, E. B. ix. 81, t. 1446. Nyman, 678. Fl. 



Oxf. 279. 

 Colonist. Lacustral. Streams and ponds, ditches, &c. Widely dis- 

 tributed, but less common in our larger streams than formerly. 

 P. May-September. 

 First recorded in Mr. Baxters MSS. 1854. 'It has already (1858) 

 ascended the Thames as high as Eeading,' Charles Kingsley, Miscel- 

 lanies, i. 181. 

 The Canadian Water Weed, which reached its maximum of abund- 

 ance in the years 1866-1874, has now much decreased in quantity, 

 probably from the absence of the male plant. It still occurs in all our 

 districts, not only in the main streams and canals, but also in the 

 ponds and ornamental water, and in small isolated ponds on the Chalk 

 downs. In a ' dew pond * on the Ridgeway it occurred at nearly 800 feet 

 elevation, to which locality it was probably conveyed by birds. 



The female flowers are borne on long stalks which readily break off, 

 and may be occasionally seen floating on the water. 



The plant was introduced into the Oxford Botanic Garden in 1849. 

 Mr. Baxter noticed the plant in the Thames near Folly Bridge in 1853. 

 Shortly after, so rapid was the growth and extension of the plant over 

 our area, that Mrs. S. C. Hall, in 1859, writes that 'It is in this 

 neighbourhood (Eynsham) we begin to perceive the dangerous results 

 of the recent and rapid growth of the American weed. It has already 

 rendered the Thames in some parts almost impassable.' Book of the 

 Thames, 71. 



Elodea canadensis is found in all the bordering counties. 



Hh 



