334 MR. H. B. GUPPY ON THE THAMES 



out of the current; and in tins manner a considerable amount of 

 material is often caught in the surviving patches of flags near 

 the side or is embayed in a sheltered hollow in the bank, where 

 it may remain for weeks or even months. In the lower parts of 

 the Lea, between Lea Bridge and Park Lock, where the current 

 is slow and the river divided up into numerous tortuous channels, 

 large collections of drift are to be found in spring in some of 

 the bends, especially after a long succession of easterly winds. 

 Should westerly winds follow, the accumulation of weeks is 

 carried in a few days into the centre of the river, and the drift 

 proceeds once more down stream. Then, again, floods, when the 

 waters subside, leave much material stranded on the banks or in 

 their vicinity, and there it may lie for weeks or months until 

 another flood picks it up. Amongst the lesser hindrances are 

 the eddies, by which the drift may spend days in one locality. 

 Here, again, the wind is an important agent either in keeping 

 together or in dispersing the drift. This is well seen in the 

 eddies at the weirs. When the wind blows towards the weir 

 the descending drift scarcely collects in the eddy, but a wind 

 blowing from the weir confines the drift in the eddy and there it 

 accumulates. In this manner I saw a large amount of diato- 

 maceous scum, which had been gathering some days above 

 Moulsey Lock, carried over the weir in an hour or two. The 

 last obstacle to the descent of the drift is by no means the least. 

 When, to take the case of the Thames, the seeds and seed-vessels 

 reach Teddington "Weir, many of them have been probably 

 battling their way down the river for months. On being carried 

 over this weir they come within the influence of the tides, and 

 there is no saying how many times they are carried to and fro 

 in the reversing currents before they successfully pass Kichmond 

 and proceed on their way to Kew, and probably enough, when a 

 seed-vessel arrives off Gravesend, it has actually traversed the 

 distance below Teddington many times over. 



My experience of the Thames hitherto has been from Kich- 

 mond up to Sunbury Weir. By using the tow-net opposite 

 the weirs, and collecting the drift in other places where it had 

 become embayed or caught in the flag-patches, I have gathered 

 in a single day materials for months of work. Picking out 

 individual seeds or fruits or bulbs is not a method to be recom- 

 mended. It is not the way to sample the drift, as most of the 

 smaller and dark-coloured objects escape notice. The only plan 



