1782 A TEXTBOOK OF THEORETICAL BOTANY 



pollen grains are triangular or rectangular in outline, with three or four 

 germ pores. 



The gynoecium is polycarpellary, syncarpous and composed of two or 

 generally four carpels. The ovary is inferior, with two or four loculi. There 

 may be one ovule in each loculus {Circaea) or there may be numerous 

 anatropous ovules with axile placentation. 



The fruit is a capsule, a berry or a nut. Most frequently it is a capsule 

 which splits loculicidally, leaving a central column which bears the seeds. 



The seeds are non-endospermic and there is often a hairy aril. The 

 embryo is nearly straight. 



The family comprises forty genera and contains some 500 species which 

 are distributed mainly in temperate and subtropical regions though a few 

 are found right into the tropics. 



The chief anatomical feature is the presence of internal phloem which 

 may either closely adjoin the system of vascular bundles or may form small 

 medullary groups. 



The classification within the family is simple, two sub-families only 

 being recognized. The genera are distributed as follows: 



I. Trapeoideae 



The ovary is only partly inferior and possesses two loculi. The fruit is 

 thorny. Trapa. 



II. Oenotheroideae 



The ovary is truly inferior and there are from one to four loculi. 

 Epilohium, Jiissieuo, Ludwigia, Oenothera, Clarkia, Godetia, Fuchsia, 

 Lopezia. 



Trapa natans, the Water Chestnut, is an annual water plant with rhom- 

 boid floating leaves and submerged adventitious roots which are peculiar 

 in that they possess chlorophyll and assimilate. The genus is anomalous 

 in many respects and may represent an ancient type which was more widely 

 distributed in the Tertiary period. Later, to judge by fossil fruits, it 

 extended over a wide range of northern and central Europe. The fruits are 

 large, prickly nuts which are used as food in China. 



The genus Epilohiinu is the largest in the family and contains about 

 160 species, of which some nine are found in Britain. The pollination 

 mechanism is interesting. Bees and species of the Lepidoptera are chiefly 

 concerned, and, in British Epilobia, it is possible to trace a transition 

 from large-flowered species which are normally cross-pollinated by insects, 

 to small-flowered types which are usually self-pollinated. We shall refer 

 to a similar series in the genus Geranium, but it will be necessary to consider 

 this example also in some detail. 



In Epilohium augustifolium the purple-red flow^ers open between 6 and 

 7 a.m. and are completely protandrous. Nectar is secreted by the fleshy 

 green top of the ovary and is protected from rain by the bases of the fila- 

 ments which converge to form a hollow cone, which encircles the base of 



