DICHOGAMY. 



309 



promoting cross-fertilization as their separation by actual distance. In other words, 

 separation in time is as efficient as separation in space; and these flowers, though 

 structurally hermaphrodite (in that they contain both male and female organs), are 

 — as the mechanism works out — unisexual (in that only one set of organs is mature 

 at any given moment). This maturation of the sexual organs so that they are 

 capable of fertilization at different times in the same plant, is termed dichogamy 



Kg. 293.— Incompletely dichogamous Flowers. 

 1 Epilobium avgustifoliuin with protandrous flowers. 2 Ereynurus Caucasieus with protogynous flowers. 



{Uxa, apart, and yd/j,os, marriage), and we may distinguish between protogynous and 

 protandrous dichoganrby. If the stigmas are able to receive pollen, retain it, and 

 stimulate it to put out pollen-tubes at a time when the pollen in the same flower is 

 still unripe and hidden in the anthers, this particular species is termed protogynous 

 (from TrpuJTos, first, and yivii, a woman). But if the pollen is shed from the dehisced 

 anthers, whilst the stigmas in the same flower are yet immature, i.e. not susceptible 

 to pollination, then the species is said to be protandrous (irpQros, first, and Av/ip, a man). 

 In the racemose inflorescence of the Willow-herb {Epilobium angustifolium), which 

 is represented in fig. 293 ^ the upper flowers are seen to be still closed; a little 

 lower are three flowers which have just opened, the middle one being visited by a 



