Walkei' : Pond Vegetation. 



and possibly the toxic effect of substances'''" contained in tlie 

 mud. 



The chief flowering- plants occurring- in the Bramhope ponds 

 fall into two groups : — 



I. Water Margin Association. (Included in Warming's 

 Rohrsiimpfe. t) 

 Plants rooted in mud and projecting a great part of 

 their body above the water. Usually rigid, with well- 

 developed xylem and aerating tissue. Roots numerous. 

 Zonation in the following order : — i. /uncus communis. 

 2. Peplis portula and /uncus articulatus. 3. Giyceria 

 /iuitans. 4. CEnanthe /istulosa. 5. Carex vulgaris. 

 6. Eleocharis palustris. 7. Sparganiuin ramosum. 

 II. Aquatic Association. (Included in Warming's Limnaen- 

 Vereinsklasse. i) 

 Plants rooted in mud ; completely submerged or with 

 floating- leaves ; usually weak Vv^th well-developed 

 aerating tissue. Roots few. Potamogeton natans, abun- 

 dant in all the ponds, P. rufescens, occurring only in 

 ponds with clear water and shallow mud. /uncus 

 supinus occurs in clayey ponds. 



Alg^. 



The algal vegetation of the Bramhope ponds has been 

 examined from time to time during the last two years and 

 a number of well-defined groups or associations have been 

 recoofnised. Althouq;h the distribution of these associations is 



B. E. Living-ston. 'Physiological Properties of Bog- Water.' Bot- 

 Gaz., Vol. 39 (1905), p. 348. This observer cultivated Stigeoclonium (a 

 g-reen alga) in a number of different bog- waters, and concludes from his 

 results that 'there are chemical substances in at least some bog- waters 

 which affect Stigeoclonium as do poisoned solutions and solutions of high 

 osmotic pressure.' The palmella condition of Stigeoclo>iiu)}i induced by 

 cultivation in bog- water is reg-arded by Living-ston as a xerophilous 

 character, as the plant passes into this form in drying media. In a pre\ ious 

 paper (Bot. Gaz., Vol. 37, 1904, p. 383) Living-ston showed that interference 

 with absorption is not due to hig-h osmotic pressure, as ' bog waters do not 

 have an appreciably hig-her concentration of dissolved substances than 

 do the streams and lakes of the same region,' and he further remarks that 

 'it. is possible that the factor in bog- water which prevents the growth of 

 plants other than x.-rophilous ones may be the presence of unknown toxic 

 bodies. ' 



t E. V\^arming-, ' Lehrbuch d. oekologischen Pflanzeng-eog-raphie. ' 

 German edition b}- Knoblauch, Berlin, 1S96, p. 162. 

 X Ibid, p. 150. 



Naturalist, 



