ADAPTATIONS FOR INTERCROSSING. 219 



rjagrees of separation, pollen is very commonly borne from 

 plant to plant ; in hermaphrodite flowers only are more special 

 arrangements needed to secure intercrossing or a certain measure 

 of it, and in these such arrangements abound. 



406. Irregularity is one of the commonest modifications of the 

 flower (326, 337) : it is never conspicuous except in blossoms 

 visited by insects and generally fertilized by their aid ; and it 

 finds rational explanation on the score of utility in this regard. 1 



407. Dichogamy, a term introduced by C. C. Sprengel, who 

 first noticed and described it, is one of the most usual and effect- 

 ual (rather physiological than morphological) adaptations for the 

 promotion of intercrossing between hermaphrodite flowers. It 

 means that such intercrossing is brought to pass by a difference 

 in the time of maturity of anthers and stigma ; this rendering 

 dichogamous blossoms practically the same as dioecious or mon- 

 oecious in respect to fertilization, while there is the economical 

 gain that all the flowers are fertile. According to whether the 

 anthers or the stigmas are precocious, dichogamous flowers are 



Proterandrous (or Protandrous) , when the anthers mature and 

 discharge their pollen before the stigma of that blossom is recep- 

 tive of pollen ; 



Proterogynous (or Protogynous) , when the stigmas are in 

 receptive condition before the anthers have matured their pollen. 



Synanthesis* the maturing of the two sexes simultaneously or 

 nearly so, is however made to secure the same result through 

 special arrangements. 



408. Proterogyny. The Plantains, such as Plantago major and 

 P. lanceolata, are familiar instances of this in a wind-fertilized 

 genus with hermaphrodite flowers. The anthesis proceeds from 

 base to apex of the spike in regular order, and rather slowly. 

 While the anthers are still in the unopened corolla and on short 

 filaments, the long and slender hairy stigma projects from the tip 

 and is receiving pollen blown to it from neighboring plants or 



1 This did not escape the attention of Sprengel in the last century, and 

 along with it the fact that strictly terminal and also vertical flowers, whether 

 erect or suspended, are seldom irregular, while comparatively horizontal or 

 obliquely set flowers more commonly are so. The irregularity is in refer- 

 ence to a landing place for the visiting insect, or also to storage of or accessi- 

 bility to nectar, &c. 



Darwin (Forms of Flowers, 147) remarks that he does not know of a 

 single instance of an irregular flower which is wind-fertilized. 



2 Synacmy is the term proposed by A. W. Bennett, in Journal of Botany, 

 viii. (1870), 316, with its opposite, Heteracmy, f or proterandry and proterogyny. 

 The latter names, in their shorter form (protandry and protogyny), appear to 

 have originated with Hildebrand. 1867. 



