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PART I. | HISTORICAL INTRODUCTION. 25 
previous observer to the insect-visitors, based his generalisations 
upon far too few observations of insect-visits ; both his classifi- 
cation of entomophilous flowers? and his general conclusions 
concerning the fertilisers of whole families (Composite, Boraginee, 
&c.) require essential modification. In no single case do the 
observations hitherto made on anthophilous insects suffice either 
to explain the differences between nearly allied species of flowers 
or to settle the primitive conditions determining any specific 
floral character. . 
In order to attain to substantial knowledge concerning such 
determining conditions, we must modify in two respects the modes 
of investigation hitherto adopted, based upon the Knight-Darwin 
law :-— | ; 
(1) Instead of considering those flowers in which cross- 
fertilisation in case of insect-visitors is distinctly insured or in 
which self-fertilisation is distinctly opposed, we must look upon all 
entomophilous flowers without exception as requiring elucidation 
to the same degree; and in each species we must consider the 
possible or inevitable occurrence of self-fertilisation in absence of 
msects with as much care as the certainty or possibility of cross- 
fertilisation in case of insect-visits. 
(2) Instead of confining ourselves to the investigation of floral 
mechanisms or of at most ascertaining in a general way by what 
groups of insects a particular plant is visited and cross-fertilised, 
“we must consider the insect-visitors with as much care as the 
flowers visited by them, We must compile for each species of 
flower a list as complete as possible of its visitors, in order to come 
by wide comparison to a safe conclusion regarding what: effect 
peculiarities in colour, odour, the secretion and concealment of the 
honey, etc., have upon insect-visits, and so upon the fertilisation of 
the plant. We must also take note of the way in which the 
insects are fitted to obtain their floral diet, and we must try to 
trace the gradual evolution of such adaptations through all stages, 
since many characters of flowers and of their visitors (e.g. length 
of tube and length of proboscis) have been developed in reciprocal 
adaptation, and can therefore only be understood when considered 
together. | 
This is the path which I have sought to enter on in the present 
book. How far I have succeeded in my task is for others to 
decide. To permit of fair judgment, I must myself explain certain 
omissions in my work. 
1 Supra, p. 15. 
