I IO 
DISTRIBUTION OF SEEDS 
In the regular methods of seed-dispersal, we find four 
agents that may be employed — wind, water, animals, and 
propulsive mechanisms upon the parent plant itself. 
The unicellular spores of ferns, &c. float in the air like dust. The 
nearest approach to this in seed-plants is in the Orchidaceae, whose 
seeds are extremely small and light. Pyrola and many Caryophyllaceae, 
&c. have also very light seeds. A number of plants with dry fruits 
have what may be termed ‘censer’ mechanisms. The fruit opens so 
far as to leave the seeds room to escape, but in such a way that they can 
only escape when the fruit is violently shaken, i.e. as a rule, only when 
a strong wind is blowing; thus they have a good chance of being carried 
some distance. Such fruits are the capsules of most Liliaceae, Iridaceae, 
Caryophyllaceae, &c., the fruits of Aconitum, Helianthus, &c. The 
seeds are liable to damage from rain in an open fruit of this kind ; some 
close when it rains, others only open by narrow protected openings, 
e.g. Papaver, Campanula. In Tulipa, Iris, &c., the seeds are flattened, 
thus increasing the surface exposed to the air without increasing their 
weight. In Pinus, Deutzia, Gordonia, Zanonia, Millingtonia, &c., the 
seed is winged as well as more or less flattened, and may be carried to 
some distance before reaching the ground. In Fraxinus, Liriodendron, 
Acer, many Malpighiaceae, Serjania, Seguieria, Ptelea, Ulmus, Paliu- 
rus, Ventilago, Abronia, Tripteris, Terminalia, Pterocarpus, Centrolo- 
bium, &c. , the wings are on the fruit, outgrowths of the pericarp. In 
Bougainvillea, Spinacia, Mirabilis, Carpinus, &c., the bracts or brac- 
teoles form the wings, in Triplaris, Armeria, Davilla, Rumex, Diptero- 
carpaceae, Trifolium sp., &c., the perianth, or part of it. In Rhus 
Cotinus , Spinifex, &c., the fruit-head is rolled bodily about by the wind 
(cf. Selaginella sp., Anastatica). A great number of seeds and fruits 
exhibit very perfect ‘ parachute * mechanisms in the form of tufts or 
coverings of hairs, e.g. the seeds of Salix, Gossypium, Epilobium, many 
Apocynaceae and Asclepiadaceae, Aeschynanthus, &c. ; the achene 
fruits of Eriophorum, Typha, Anemone, Compositae, &c. ; in Clematis 
the style becomes hairy alter fertilisation. 
Adaptations to water-carriage are found in a few water-plants 
(Chap. III.), and in Veronica sp., & c. 
Animal distribution is of two kinds — inside or outside the animal. 
To the former class belong all fleshy fruits; these are eaten and the 
seeds afterwards dropped. The seeds must be able to pass uninjured 
through the alimentary canal. This is usually effected by means of 
a hard covering, the seed-coat in berries, the endocarp in drupes. In 
some cases the seed is sticky, e.g. in Viscum, and is ejected by the 
bird ; in Strychnos, &c., it is poisonous. Most fleshy fruits are dis- 
tributed by birds and are found on shrubs and trees; comparatively few 
are eaten by other animals. They are commonly brightly coloured 
when ripe, and so attract notice (cf. flowers). In Anthurium, Magnolia, 
Acacia sp., &c., special arrangements increasing the conspicuousness 
are found. The seeds of Abrus, Adenanthera, Ricinus, &c., and the 
fruits of Scorpiurus, Biserrula, &c., resemble beetles or caterpillars, and 
it is often suggested that birds are deceived by them and carry them to 
