194 THE RING OF NATURE 



whatever brushes against them as they sit ripe on 

 their stalks. We only have to walk through a 

 field, or better still through a wood, to find our 

 legs or skirt covered with what we generally regard 

 in a lump as burrs. Some are harder to get off 

 than others, and that is all that most of us care 

 to know about them. There are galium, hound's- 

 tongue, dog's mercury, avens, agrimony, corn- 

 buttercup, enchanter's nightshade and a hundred 

 others. The boy scout merely takes a glance at 

 your trouser-leg and knows the very field you have 

 been in, while you are quite unaware of the terrible 

 infection you may be carrying. You and your 

 spaniel jump into a train, thence into a ship, and 

 perhaps girdle half the world before the seeds on 

 your clothes or pelt fall off and come into their 

 new kingdom. 



The burr has scarcely yet been evolved that will 

 stick to the feathers of a bird. The genus Trapella 

 gives one excellent example, but curiously enough 

 that plant is one of the rarest and most local of 

 plants. On the other hand, the plants that are 

 most widely distributed throughout the world seem 

 to be highly qualified in another way to get their 

 seeds carried by birds. 



The three commonest plants throughout the 

 world are probably purple loosestrife (Lythrum 

 salicaria), gipsy wort (Lycopus europceus), and self- 

 heal (Prunella vulgaris). I must leave the reader 

 to fathom the secret of the gipsy wort. Prunella 

 will be found to have a sticky fruit against which 



