DISTRIBUTION OF SEEDS 
hi 
a distance before finding out the mistake. Carriage of seeds or fruits 
by the outer surface of the animal’s body is usually effected by hooks. 
Hooked seeds are very rare ; they occur in Villarsia, &c. Hooked 
fruits (burs) are common ; the hooks may be on any part of the fruit 
proper or on the accessory organs — receptacle, corolla, &c. (e.g. cf. 
Bidens, Tragoceros, and Xanthium, in Compositae). Examples are 
Triglochin, Uncinia, Cenchrus, Emex, Triumfetta, Bunias, Agrimonia, 
Acaena, Geum, Medicago, Circaea, Blumenbachia, Sanicula, Daucus, 
Galium, Asperula, Cynoglossum, Martynia, Harpagophytum, &c. In 
Tribulus, &c. , the fruit has hard spines and lies upon the soil till trodden 
on by an animal and is then carried away sticking in its foot. In Arc- 
tium the hooks cling to passing animals and finally let go their hold 
and the plant swings back jerking out the fruits. In Allionia, Pisonia, 
Plumbago, Siegesbeckia, &c., the fruit clings by glandular hairs. 
Propulsive mechanisms in the fruit itself may be of two kinds. In 
Dorstenia, Oxalis, Impatiens, Cyclanthera, Ecballium, &c., the pro- 
pulsion depends upon extreme turgidity in some part of the fruit. In 
Lupinus, Ulex, Eschscholtzia, Scandix, Euphorbia, Ricinus, Hura, 
Acanthaceae, Alstroemeria, Cardamine, Buxus, Claytonia, Viola, Gera- 
nium, &c., tensions are set up by the drying of certain parts of the 
fruit-tissue when exposed to the air. 
Observation shows that as a rule none of the mechanisms transport 
seeds or fruits to great distances ; a few hundred yards is usually the 
maximum. This, however, is probably sufficient to gain all the advan- 
tages of seed-dispersal. 
In studying the mechanisms of seed-dispersal, the morphology of the 
various fruits should be compared, so as to notice how in different fruits 
the same end is attained in different ways; e.g . how the testa, aril, 
gynoeceum wall, receptacle, corolla or perianth may be fleshy, or 
hooked, &c. It should also be noted that there is much greater variety 
in this respect among nearly allied forms than there is in the general 
floral mechanism. This goes to show that the seed-dispersal methods 
are of recent acquirement. Such orders as Cruciferae, Compositae, 
Leguminosae, Rosaceae, Umbelliferae, and such genera as Trifolium, 
Valerianella, &c., are of special interest in this connection. See Part 
II., and Chap. III. (especially under Epiphytes) 1 . 
Germination. Placed under suitable conditions — 
darkness, moisture, supply of oxygen, and suitable tem- 
perature — the seed germinates (Fig. i, p. 37). The testa is 
burst by the swelling of the seed, the radicle is pushed out, 
at or near the micropyle, by the lengthening of the hypo- 
cotyl, and grows down into the soil as the root. The 
plumule presently comes above ground, often bent back 
on itself like a hook, and begins to develope into the young 
1 Hildebrand, Verbreitungsmittel der Pjlanzen, Leipzig, 1873 ; 
Darwin, Origin of Species ; Kerner, Natural History of Plants . 
Literature to 1890 indexed by MacLeod in Bot. Jaarb., Gent 1891. 
