xi LETTERS TO MARCO 67 



of gas bubbles evolved from the growth. 

 This small water- moss, or whatever it is, as 

 the gas bubbles accumulate, gets buoyed up 

 from the bottom of the river, carrying with it 

 some of the soil attached to the rootlets ; in 

 ponds one often sees this stuff, which at last 

 accumulates on the surface in a disagreeable 

 way, but on the river it floats down and trans- 

 plants itself with its little mass of travelling 

 soil. I have very little doubt it rises thus to 

 the top, as some larger water - weeds do, 

 during its blooming period, and sinks again 

 to the bottom for the winter. If you squeeze 

 one of these lumps, so as to set the bubbles 

 at liberty, it will sink directly. 



September is just the month for spiders, 

 and I get much amusement from watching 

 them. In the boat-house there is a grated 

 window which does not open, and, being out 

 of the way, is entirely given up to the spiders ; 

 every corner of it and of the embrasure has 

 numberless cobwebs, whilst across and across 

 in every direction the wheel webs are spun 



