1 58 CHENOPODIUM, POLYGONUM. [chap. 



the Aristolochiaceae ; two orders which in many re- 

 spects form a marked contrast to the remainder, and 

 have, at least in some species, conspicuous flowers. 

 In the other orders, on the contrary, the flowers are 

 generally minute. Thus in the Paronychiaceae, 

 Bentham says, " Petals usually none, or represented 

 by five small filaments ; " in Santalaceae, " flowers 

 small ;" in Empetraces, flowers " minute, axillary ; " 

 in Callitrichines, flowers " minute ; " in Urticacese, 

 flowers ''small;" in Ulmacese, flowers "small;" 

 while in the Amentaceae (beech, oak, birch, &c.), and 

 Coniferae, the flowers rarely are coloured, or contain 

 honey. Indeed, it is, I think, a strong argument in 

 favour of Sprengel's views, that while large flowers 

 are almost always coloured, small ones are usually 

 greenish ; thus out of thirty-nine British genera of 

 Incompletse, by far the greater number of which have 

 small flowers, in no less than thirty-seven genera they 

 are also more or less greenish. 



In the Polygonacese, the species of the genus 

 Rumex are wind-fertilised ; occasionally, however, 

 visited by insects. 



The species of Polygonum differ considerably 

 from one another in the mode of their fertilisation. 

 Some, as, for instance, P. aviculare (Knotweed), have 

 small inconspicuous flowers, and very little, if any 

 honey. They are consequently but seldom visited by 

 insects. Other species, on the contrary, such as P. 

 Fagopyrum (the Buckwheat), and P. Bistorta, are 

 much more conspicuous, contain honey, and are 

 fertilised by insects. These species, however, also 

 differ considerably ; P. Bistorta is proterandrous 



