28 INTRODUCTION 



observations. On the other hand, processes of pollination that were not 

 described by Miiller, and plants investigated by later observers, are treated at 

 somewhat greater length. Occasionally, Loew goes back to older publications 

 when this seems necessary for the completion of his accounts. Owing to the 

 exigencies of space, lists of visitors had to be excluded, but in the case of 

 certain plants at least the chief groups of the flower visitors are given, together 

 with an enumeration of species. Loew's ' Blutenbiologische Floristik ' has been 

 an indispensable work of reference for me during the production of this work, 

 and many facts have been taken from it. 



SECOND SECTION 



PRESENT STANDPOINT OF FLOWER POLLINATION 



I. Survey of the Modes of Pollination and of the 

 Distribution of the Sexes. 



The following chief kinds of pollination and fertilization are known to us at 

 the present time : — 



(I) Autogamy (Delpino), or Self-pollination : the pollen reaches the stigma 

 of the same flower. Autogamy is therefore only possible in hermaphrodite flowers. 

 When effective the result is Autocarpy, or Self-fertility ; if not effective. Self- 

 sterility. 



(a) Direct Autogamy (Spontaneous Self-pollination) depends upon the relative 

 positions of stigma and anthers, without reference to external agency. 

 If it is effective the result is Direct Autocarpy. 



(h) Indirect Autogamy (Self-pollination in the narrower sense) is brought about 

 by external agency. If eflfective the result is Indirect Autocarpy. 



(II) Allogamy (Kerner), or Cross-pollination. The pollen reaches the stigma 

 of another flower. If effective the result is Allocarpy ; if non-effective there is 

 Adynamandry. 



(a) Geitonogamy (Kerner), or Pollination by a neighbour, occurs between 

 flowers of the same plant. If it is effective the result is Geitonocarpy. 



(3) Xenogamy (Kerner), or Crossing, occurs between flowers of different plants 

 of the same species. If effective the result is Xenocarpy. 



(III) Hybridization occurs between flowers of different species. If effective the 

 result is Hybridocarpy. 



The most important known ways in which the sexes are distributed, as well 

 as the various possibilities of pollination conditioned by the arrangement of stamens 

 and carpels, may be summarized as follows ' : — 



' Cf. Kirchner, ' Flora von Stuttgart' (pp. 38-40). 



