196 ALTERATION OF POSITION. 



a most abundant crop, henco these plants were acci- 

 dentally prevented from perfecting their female organs.^ 



Mr. Dar\vin' cites from various sources the following 

 details relating to strawberries which it may be useful 

 to insert in this place, as throwing some light upon 

 the production of unisexual flowers. " Several English 

 varieties, which in this country are free from any such 

 tendency, when cultivated in rich soils under the 

 climate of North America commonly produce plants 

 with separate sexes. Thus, a whole acre of Keen's 

 seedlings in the United States has been observed to be 

 almost sterile in the absence of male flowers ; but the 

 more general rule is, that the male plants over-run the 

 females. . . . The most successful cultivators 

 in Ohio plant, for every seven rows of pistillate flowers, 

 one row of hermaphrodites, which afford pollen for 

 both kinds ; but the hermaphrodites, owing to their 

 expenditure in the production of pollen, bear less fruit 

 than the female plants." 



Stratiotes aloides has been said to produce its carpels 

 with greater abundance towards the northern limits 

 of its geographical distribution, and its stamens, on 

 the other hand, are stated to be more frequently de- 

 veloped in more southern districts. 



Honclcenyapeploides affords another illustration of the 

 sexual arrangements in the flower being altered as it 

 would seem by climatal conditions. Thus, in the 

 United States, according to Professor Asa Gray, the 

 flowers are frequently hermaphrodite, while in this 

 country they are usually sub-dicecious.^ 



Treviranus"* says that the flowers of Hippuris and 

 Callitriche are apt to be hermaphrodite in summer, but 

 female only at a later period. 



For further remarks on this subject, see sections 

 relating to suppression of stamens and pistils. 



' Thomson, ' Gardener's Assistant,' p. 577. 

 ' ' Variation of Animals and Plants,' i, 353. 



* Babington. ' Ann. Nat. Hist.,' vol. ix, 1852, p. 156. 



* ' Phys. der Gewachse,' ii. p. 323. 



