162 HOUSE, GARDEN, AND FIELD 



relationship that causes these plants to look so much alike. 

 Do they profit by their resemblance to the stinging nettle, 

 being mistaken for it and so let alone ? Is there anything 

 in the shape of the leaf particularly appropriate to a plant 

 which is shaded on one side and tolerably illuminated on 

 the other ? Has this shape of leaf anything to do with 

 rain -drip, or with bud-packing ? I have put such questions 

 to myself for many years, but cannot answer them. 



THE DITCH. 



The ditch beneath the hedge is partly dry and partly 

 wet. Where it receives the oozing from a bog in the next 

 field, it always has standing water in it, and the little pool 

 thus formed is a great resource to us, for there are no 

 ponds nor any other bit of standing water near at hand. 

 The ditch yields us three flowering plants (duckweed, 

 float-grass, and starwort), tadpoles, pond-snails, and a 

 great number of microscopic organisms. Duckweed I 

 have already written about ; 1 of starwort I have nothing 

 to tell as yet ; some account of the leaves of float-grass 

 will be found on p. 267. 



MOLLUSKS OF THE DlTCH. 



Two species of mollusks abound in the ditch ; one of 

 these (Cyclas cornea) is a bivalve ; the other is a water- 

 snail with a spiral shell (Limnaea peregra). What are the 

 most convenient names for these two mollusks ? I cannot 

 bring myself to call Cyclas a freshwater cockle, as some do, 

 because that is a name which must be unlearned by every- 

 body who comes to know what a cockle really is. Perhaps 

 we may tolerate the not very difficult Greek name, Cyclas ; 

 pond-snail will do for the various kinds of Limnaea, if we 

 are careful to use it for no others ; peregra means travelling, 

 and the name of travelling pond-snail will distinguish the 

 species found in our ditch from all others. 



Cyclas, which is also called Sphaerium (what a plague to 



1 Round the Year y p. 192. 



