348 BRITISH FLOWERING PLANTS chap. 



P. amphibium.- — Tliis species secretes honey by five 

 orange-yellow glands at the base of the ovary. The 

 flowers are dimorphous ; some with a long pistil and 

 short stamens, others with long stamens and a short 

 pistil. There are also female flowers. The plant grows 

 sometimes on land and sometimes in water. And here 

 we find also another interesting adaptation. The land 

 form is more or less hairy, while plants growing in water 

 are entirely glabrous. One form changes into the other 

 if the plant is moved from dry land into water or 

 vice versa. 



P. Hydropiper. — The flowers are small and without 

 nectar. Of the eight stamens two are generally rudi- 

 mentary. Some of the flowers in this and the following 

 species are cleistogamous, especially those which receive 

 little light. The plant is protected from browsing 

 quadrupeds by a bitter juice, whence the name. 



P. minus is very near the preceding. It has no 

 bitter flavour, but is probably protected by its great 

 similarity to P. Hydropiper. Bentham regards it as a 

 mere variety. 



P. Aviculare (Knot-grass). — A creeping plant with 

 small green, white, or purple flowers which have no 

 scent or honey. Five of the eight stamens bend out- 

 wards towards the corolla ; the other three towards the 

 stigma, which, as they are at the same level, and ripe 

 at the same time, they can scarcely fail to fertilise. 

 The young leaves rise up vertically at night. 



P. Fagopyrum (Buckwheat). — This is an Asiatic 

 species, but familiar to us as being so often cultivated. 

 The flowers are markedly dimorphous. According to 

 Eicher they are quite sterile when self- pollinated, or 

 with pollen from flowers of the same form on the same 

 plant. They are very slightly fertile after cross-pol- 

 lination between flowers of the same form on distinct 

 plants. They are, on the contrary, highly fertile after 

 cross-pollination between flowers of difi'erent form on 

 distinct plants.^ 



' Comptes Sendus, cxxxviii. (1904). 



