130 BOTANY. [chap. iv. 



ing plants — Angiosperms — that we meet with the roost 

 profound modifications of the flower for the purpose of 

 securing cross-fertilization, insects being the agents em- 

 ployed in transferring the pollen from one plant to the 

 stigma of another plant of the same kind, and in this 

 group of plants the present form, colour, and fragrance 

 of flowers, also the secretion of nectar has gradually 

 evolved through the unconscious selection exercised by 

 insects in their search for food, which is furnished by 

 the sugary liquid or nectar present in many flowers, and 

 this object is the only one the insect has in view, the 

 transportation of pollen being an entirely unconscious 

 act ; and although in many plants that are visited by 

 insects, the chances of meeting with nectar are uncertain 

 as is the chance of cross-fertilization, yet in numerous 

 other instances the modifications that have taken place in 

 both the flower and the insect have resulted in what may 

 be called mutualism, differing only from the mutualism 

 between algae and fungi that form lichens in the two 

 organisms retaining their individuality and liberty of 

 action, yet so thoroughly interdependent that their indi- 

 vidual existence depends equally on the existence of 

 both ; that is, there are certain plants that have become 

 so . thoroughly modified that fertilization can only be 

 effected by particular insects, the latter in turn being 

 able to obtain their food alone from the flower they can 

 fertilize. Looking at such a case of perfected mutualism 

 as that just indicated, naturally supports the old idea 

 of a preconceived arrangement and special creation of 

 two distinct forms of life adapted from the first to 

 mutually assist each other, but when we see on every 

 hand other forms of life exhibiting every phase from the 



