724 NATURAL SCIENCE. dec. 



me-not (Myosotis palusti'is) and other plants are present in numbers 

 with shoots and buds of several of the Potamogetons and the arrow- 

 head. Many grub-cases are found, and numerous other minute forms 

 of life. 



Collections from the drift of the Thames and Lea have much 

 the same composition. From October, when seeds and fruits first 

 begin to accumulate in any quantity, through the winter to February 

 and March, there are always to be found floating in these rivers, 

 usually in numbers, the achenes of Ranunculus repens andi?. scelevatus ; 

 the nuts of Lycopus curopcdus and Scutellaria galericulata ; fruits of 

 Atiiplex patula, and several species of Ruim.x; the mericarpsof /l^o'^/u'rt; 

 the nuts of the alder and birch ; the drupes oi Sparganium raiiiosuiii, the 

 carpels of the water plantain, and the fruits of different species of Gz/r.r. 

 Less frequent are the black carpels of Galium palustvc, and the seeds 

 of the yellow flag. The Thames is distinguished from the Lea by 

 the number of seeds of Impatiens fulva and the yellow-rattle [Rhinauthus 

 crista-galli), while fruits of Bidens are more frequent in the Lea. 

 Most of the seeds and fruits in the spring drift have floated through 

 the winter ; nuts of alder and birch, however, are continually 

 dropping from September to June ; those of the birch only float a few 

 days, and yet are plentiful in the drift during February and March. 

 Except the birch-nuts, all these seeds of the river drift germinate in 

 the water in March and April, or even before, and in nearly every 

 case the germination is completed at the surface, where the seedlings, as 

 a general rule, float and thrive, developing the first few leaves, but 

 never attaining a greater length than an inch or two, though if 

 stranded on a mud-bank they readily strike and develop the full-sized 

 plant. 



The ice of an English winter was found by Mr. Guppy not to 

 aff'ect the germinating power of the seeds in our ponds and rivers. In 

 the case of several of the above-mentioned seeds which had been 

 cased in ice for twenty days, as large a proportion germinated ao 

 when they were not thus enclosed. In the shallow water of the Lea 

 when the water was frozen to the bottom, the underlying mud was 

 also frozen for an inch or so, coming up in a continuous mass with the 

 ice ; and shoots of forget-me-not taken up in this manner are still alive. 

 Though the power of germination is unaffected, great numbers of 

 the seeds and fruits sink to the bottom after the thaw, the ice 

 affecting the vitality of the outer coverings or buoyant parts of the 

 fruit, a process which is a direct aid to germination in the case of 

 Sparganium ramosuni and Potamogeton natans. The ice also sends to 

 the bottom about half the fronds of the floating duck-weed ; in fact, 

 it may be generally stated that after a thaw the river is cleared 

 of a large proportion of the drift. 



When a germinating seed gets enclosed in ice, germination is 

 arrested; but after the thaw the process is often rapidly completed, 

 and a diminutive seedling prematurely discharged. This occurs, for 



