AS AN AGENT IK PLANT DISPERSAL. 345 



to the outside of the fruit. This material would be very likely 



to adhere to the plumage of a bird sitting in the water, and on 



its drying the seeds in it would be firmly attached to the 

 feath 



ers. 



Floating in numbers in the drift of the Thames and the Lea 

 and of the ponds of Epping Forest from the autumn on through 

 the winter to the spring occur the detached leaflets of Carda- 

 mine hirsuta. I have kept some afloat the winter through, and 

 have obtained plants from them in the spring. I have plants 

 grown irom leaflets found floating in the Lea in February, and 

 am now growing plants from leaflets found floating in the 

 Thames in January and February, and also plants from leaflets 

 that have been some weeks in ice. A week in sea-water destroys 

 the reproductive power of the leaflet ; nor do they seem to 

 withstand drying, for the wind might be a very important agent 

 in transporting the dried-up leaflet ; but my experiments on this 

 matter are not yet complete, and my notes on this plant have not 

 yet been put into shape in consequence. 



Lastly, I come to the Lemna, as characteristic of our rivers as 

 of our ponds and ditches. In botanical textbooks reference is 

 made to the disappearance or sinking of the fronds in autumn. 

 Lemna minor fronds collected in the Lea in October remained 

 at the surface through the w r inter, and are now thriving. I 

 found the fronds during every month of the year, either in a 

 river or in a pond or ditch. Sometimes I have found them in 

 quantity inclosed in ice, as in the ponds of Epping Forest in 

 the middle of December. Seeds that 1 found floating in February 

 in the river Lea and in an Edmonton ditch germinated in March 

 and reproduced the plant. The seeds will germinate after 

 floating a day or two in sea-water, but a week's immersion 

 kills them. Sea- water kills most of the fronds, even after a day's 

 flotation ; but some recover, and in one or two rare instances 

 survived a week in the sea. The fronds do not survive twenty- 

 tour hours' drying in fine weather, whether in the sun or in the 

 shade ; but in rainy weather they can withstand an exposure of 

 one or two days, and might thus be carried a few hundred miles 

 entangled by their rootlets in a bird's plumage. Lemna gibba 

 apparently disappears in the winter, a lew dead fronds only 

 coming under my notice. Lemna polyrrhiza is represented ia 

 the winter by small single rootless tronds quite different in ap- 

 pearance from the characteristic fronds of the spring and summer. 



LINN. JOUIIN. — BOTANY, VOL. XXIX. 2 C 



