126 Chapters in Modern Botany chap. 



sequently a diminished stress upon the external selection 

 which plays upon this. 



Hence we have all sympathy with a recent critic, Dr. 

 Jumelle, who, in reviewing a recent endeavour to explain 

 not only the presence but the position of alkaloids, etc., in 

 plants by showing how defensive they are, says : " The 

 final causes to which so many authors constantly appeal, 

 have indeed the advantage of supplying an easy explana- 

 tion of embarrassing facts, but they are hurtful to the 

 progress of science, since the mind duped by an illusory 

 satisfaction is dissuaded from further investigation." 



Plants and Ants. — Both gardeners and botanists have 

 long been aware that ants are among the most frequent 

 guests of flowering plants, and such names as Mynnecodia, 

 Euphorbia forniicaruni^ refer to this. Are these visitors 

 hurtful ? In most cases only to a slight extent, for although 

 they rob the flowers of honey, they compensate for this by 

 eating other small insects which would do the plants much 

 harm. They are useful to the plant but not to its flowers, 

 for as the worker-ants are not winged, they are not suited 

 for carrying the fertilising pollen from plant to plant as 

 bees and flies often do. They devour pollen and nectar 

 without fulfilling any useful function, and it is said that 

 when there are crowds of them about a flower the bees are 

 apt to have their noses somewhat rudely pulled when they 

 thrust them into the recesses of the flower, and this will 

 obviously tend to frighten away the bees. But without 

 attaching much importance to this allegation that the ants 

 assault the bees, we see that it is advantageous that the 

 ants should be excluded from the flowers. In many plants 

 this is effectively done. There may be, as in some of the 

 teasel tribe, chevaux-de-frise of stifl", downward -pointing 

 hairs, like those inside of a pitcher plant, against which the 

 ants cannot climb. There may be sticky parts of the stem 



