6 THE STRUCTURE OF FLOWERS. 



There is another point which may be here noticed. That 

 a flower-bnd is a metamorphosed leaf-bud is now an accepted 

 fact ; but an obvious difference between thera consists in the 

 arrested state of the axis of tbe former, constituting the floral 

 receptacle ; and the question arises, how has this arrest been 

 brought about ? Like all other peculiarities of structure 

 to be described, I would attribute the arrest primarily to the 

 altered nature of the foliar organs on becoming members 

 of flowers. Thus, a Fir-cone and a Buttercup are arrested 

 branches ; but when the parts of a flower are reduced ia 

 number, and instead of being in a continuous spiral are 

 grouped in " compressed cycles," * I would then (hypo^ 

 thetically) attribute this further reduction of the axis, as 

 well as other features hereafter to be described, to the 

 irritation of insects in probing for juices, and causing 

 nectaries to be formed, f It is the commonest thing for leaf- 

 buds to be arrested, and sometimes metamorphosed as well, 

 by insects puncturing and depositing their eggs in them. 

 Such may be seen on the terminal shoots of Yews, Thyme, 

 and in certain kinds of Oak-galls, etc. In all such cases the 

 immediate effect is the total arrest of the axis, though the 

 leaves may be but slightly altered, as in the Yew. How 

 the various metamorphoses of leaves into petals, etc., has 

 followed will be discussed later on. 



It must not be forgotten, however, that the tendency to 

 shorten the axis is primarily, in some cases, due to the 

 altered structure of the foliar organs, as in Gymnosperms ; 

 whereby they undertake the reproductive functions. At 

 the same time, I think insects have had a good deal to do 

 with it, in many other phanerogams, Avhich have but few 

 pai'ts to their Avhoi-ls. 



Each of the above principles must now be considered in 

 detail. 



* See pp. 41, 42. t See p. 140, seqq. 



