SOxME PLANT BIOGRAPHIES. 191 



spirally round them, and so enable the vetch to 

 climb up bodily in spite of its weak stem, and raise 

 its leaves and flowers to the air and the sunlight. 



At the base of every leaf, again, you will find, 

 if you look, two arrow-shaped appendages, which 

 block the way up the stem towards the developing 

 flowers for useless creeping insects such as steal 

 the honey without assisting fertilisation. On each 

 appendage is a curious black spot, the use or 

 function of which is not apparent while the blos- 

 soms are in the bud. But after a few weeks' 

 growth, the vetch begins to produce solitary 

 flowers in the angle of each upper leaf ; flowers 

 of the usual pea-blossom type, but pink or red- 

 dish purple, and handsome or attractive. These 

 flowers contain abundant honey to allure the 

 proper fertilising insects. Just as they open, 

 however, the black spot on the arrow-headed 

 appendages of the lower leaves, in whose angles 

 there are no flowers, begins also to secrete a little 

 drop of honey. 



What is the use of this device ? Well, if you 

 watch the vetch carefully, you will soon see that 

 ants, enticed by the smell of honey in the open- 

 ing flowers, crawl up the stem in hopes of steal- 

 ing it. But ants, as we know, are thieves, not 

 fertilisers. As soon as they reach the first black 

 spot, they stop and lick up the honey secreted 

 by the gland, and then try to pass on to the next 

 appendage above it. But the arrow-shaped barbs, 

 turned back against the stem, block their further 

 progress ; and even if they manage to squeeze 

 themselves through with an effort, they are met 

 just above by another honey-gland and another 

 barrier in the shape of a second arrow-shaped ap- 

 pendage. No ant ever gets beyond the third or 



