CHAPTER XXIV 



THE ANGIOSPERMAE : POLLINATION; AN 

 INTRODUCTION TO FLORAL BIOLOGY 



When we speak of floral Biology we imply the study, both by observa- 

 tional and experimental means, of all the phenomena of organization and 

 function in the flower which serve, either directly or indirectly, the transfer 

 of conspecific pollen from anther to stigma. The term " Floral Biology " 

 is obviouslv not an ideal one, for it seems to suggest more than is covered 

 by the above definition, but it is now firmly fixed in botanical terminology 

 with this acceptation: the process of pollination. The term "flower", 

 also, must here be understood in a biological rather than a morphological 

 sense, as applying to any floral organization which functions as a unit for 

 purposes of pollination, whatever its morphological nature may be. 



The subject is one in which a critical outlook is essential, for the inter- 

 pretation of floral structures from a functional standpoint abounds in pit- 

 falls. In no other study, perhaps, is there a greater temptation to use teleo- 

 logical ideas and expressions, and in unscientific hands it has often become 

 a mere hunt for supposed " adaptations". 



That the harmonies called adaptations exist must be admitted by the 

 most critical. Many complex floral structures can be understood in no 

 other way, such as the relationship of the structure of the Strelitzia flower 

 to polHnation by birds (see p. 1300), but of the history of these structures 

 we know nothing, and we must not rashly assume that because a certain 

 structure is related to a certain function, the structure was developed with 

 that end in view. That is the essence of teleological adaptationism and it 

 should be abjured in favour of the strictly guarded conclusions derivable 

 from observation and experiment. Only in the sense of an observed har- 

 mony between structure and function can we speak of an adaptation existing. 

 The word itself should indeed be avoided as much as possible, for it conveys 

 the dangerous idea of " making-fit-for ", of which we should beware. 



The separation of microspores and megaspores on diff"erent members of 

 the flower, combined with the retention of the megaspore in the mega- 

 sporangium, makes pollination a necessary preliminary to fertilization, except 

 in the special case of cleistogamous flowers of which we shall speak later. 

 It is thus a process confined to the Spermatophyta. An analogy may be 

 found in the conveyance of antherozoids to the neighbourhood of the 

 archegonium in dioecious Bryophyta, which also involves agencies beyond 

 the mobility of the antherozoids themselves; but about these we know very 

 little. 



Only a small minority of flowers are pollinated by their own pollen as a 



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