284 FEETILISATION IN FLOWERING PLANTS. 



valves, which are covered with pollen-grains. The species of Stylidium 

 have their anthers and stigma seated on a column, the base of which 

 is slightly swollen and irritable. When a stimulus is applied, this 

 column passes with considerable force from one side of the flower to 

 the other, rupturing the anther-lobes, and thus aiding in fertilisation. 

 In some plants the pollen is scattered by the wind, and they are 

 called anemophilous (avif/jo;, wind, and p/Xos, love) ; whUe in other cases 

 animals are the agents employed in its distribution, and the plants 

 are called zoophilous (^<io\i, animal). It has been ascertained that 

 self-fertUisation is by no means common in flowers, that Is to say, the 

 pollen is not always applied to the pistil of the flower in which it is 

 produced. We constantly find that pollen produced by the anther of 

 one flower is applied by the medium of wind or insects to the pistil 

 of another flower on the same plant, or on difierent plants. This is 

 seen very evidently in monoecious and dioecious plants. It also occurs 

 in dimorphic plants where there is a difierence in the development of 

 the stamens and pistil in the case of individual flowers ; as is well 

 seen in some species of Primula, and of Linum. Flowers visited 

 by insects are often highly coloured and odoriferous, and secrete 

 honey-like matter. Night-flowering and night-smelling plants attract 

 crepuscular insects. These may be illustrated by Pelargonium triste, 

 Hesperis tristis, and Nyctanthus Arbor-tristis. Stapelias (carrion 

 flowers) by the fetid odour of their flowers attract blow-flies, which 

 deposit their eggs amongst the hairs of the flower. The eggs in due 

 time are hatched, and then the maggots in search of food press the poUen 

 masses downwards to the stigma and so cause fertilisation. In Oxalis 

 Acetosella the flower is erect during the day, and is open to the visits 

 of insects; it describes an arc of more than 100 degrees when the 

 sun sets, and flnaUy has its opening directed to the ground. 



The poUen in the case of plants fertilised by insects is sometimes 

 elliptical with three or more longitudinal furrows, as in Ranunculus 

 Ficaria, Aucuba japonica, and Bryonia dioica ; at other times it is 

 spherical or elliptical, and covered with projecting processes (echinate), 

 as in many Oompositse, Malvacese, and Cucurbitacese; or, thirdly, the 

 pollen grains are attached together by threads or a viscid secretion, 

 as in Eichardia Rhododendron and (Enothera. In plants fertilised by 

 the wind, as in most grasses, Hazel and Populus balsamifera, the 

 pollen is almost perfectly spherical, and has no processes, and is 

 generally light and dry. Dr. Dyer remarks that while in Cmciferae 

 fertilisation is generally effected by insects, in Pringlea antiscorbutica 

 (Kerguelen Island Cabbage), which differs from the plants of the order 

 in having no petals, no honey glands, an exserted style and papillose 

 stigma, fertilisation is effected by the wind. It has been stated by some 

 authors that in the case of the cereal grains impregnation is effected 

 before the flowers are open, and that thus self-fertUisation takes place. 



