HETEROGAMY. 191 



tually suppressed, a tendency towards structural com- 

 pleteness rather than the reverse. It must be also 

 understood that the following remarks apply to struc- 

 tural points only, and are not intended to include 

 the question of function. The occurrence of hetero- 

 morphic unions renders it necessary to keep in mind 

 that plants hermaphrodite as to structure are by no 

 means necessarily so as to function. 



The simplest case of this alteration in the relative 

 position of the sexes is that which occurs in monoecious 

 plants, where the male and female flowers have a definite 

 position, but which in exceptional instances is altered. 



Change in the relative position of male and female flowers 

 may thus occur in any moncecious plant. Cultivated 

 maize, Zea Mays^ frequently exhibits alterations of this 

 kind; under ordinary circumstances, the male inflor- 

 escence is a compound spike, occupying the extremity 

 of the stem, while the female flowers are borne in 

 simple spikes at a lower level, but specimens may now 

 and then be found where the sexes are mixed in the 

 same inflorescence ; the upper branching panicle 

 usually containing male flowers only, under these 

 circumstances, bears female flowers also.^ In Hke 

 manner, but less frequently, the female inflorescence 

 occasionally produces male flowers as well. 



Among the species of Carex it is a common thing 

 for the terminal spike to consist of male flowers at the 

 top, and female flowers at the base ; the converse of 

 this, where the female flowers are at the summit of the 

 spike, is much more uncommon. An illustration of 

 this occurrence is given in the figure (fig, 100). 

 Among the Coniferce numerous instances have been 

 recorded of the presence of male and female flowers 

 on the same spike, thus Mr. now Professor Alexander 

 Dickson exhibited at the Botanical Society of Edinburgh 



' See also Clos., 'Mem. Acad. Toulouse,' sixth ser., t. iii, pp. 294 305. 

 Scott, ' Trans. Bot. Soc. Edinburgh,' t. viii, p. 60. Wigand, ' Flora,' 

 1856. p. 707. 



