OXFORD: THE UPPER RIVER 199 



spersed among the leaves are each provided with a 

 trap-door. Should any prying larva or inquisitive little 

 fry look in at the door in passing, his fate is sealed. 

 He is caught, and drawn into a chamber of death 

 from which there is no escape. A plant if kept in an 

 aquarium will soon catch in this way most of the small 

 things about — for instance, tiny fish, the larvae of gnats, 

 and even Daphnia^ in spite of his shell. Drosera, the 

 sundew, drains the insects of their juices as soon as 

 they are caught. The bladderwort, on the contrary, 

 simply holds its prisoners captive till they die, and 

 then, it is said, feeds on the products of decay. 



Now we must get back to our boat. 



Look at that gaunt grey sentinel watching us from 

 over the meadow. There are always a few herons' nests 

 in Witham Woods, and this bird has come from there. 

 He is waiting for frogs, and perhaps for a water-rat 

 As soon as we are safe away he will turn to his task 

 again : lowering his head, rounding his shoulders, and 

 watching on. Here we have reached the first ford (as far 

 as I know) on the Thames. A man can walk across here 

 in summer without getting wet above his knees. The 

 ford is white with beds of water-crowfoot — a common 

 flower, but, like many common flowers, with its own 

 special interest. Nature has adapted it remarkably to 



/uvoe- .' 



.-e ChcJ-c^d 



