166 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 Empetraceae, flowers " minute, axillary;" 

 in Callitrichineae, flowers " minute ; " in Urticaceae, 

 flowers " small ; " in Ulmaceae, 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 

 Incompletae, 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 Nettle, which 

 is wind-fertilised, the anthers are provided with a 

 spring which, suddenly opening, scatter the pollen. 



In the Polygonaceae, 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 con- 

 spicuous, contain honey, and are fertilised by insects. 



