苗木育成からみた樹木種子の運搬者としての鳥類の役割について

抄録

The present paper deals with the role of fruit-eating birds as the transporters of tree seeds, from the point of view of tree nursing in northern Hokkaido.
Ornithochoryl, or seeds dispersal of trees and shrubs by birds, is a very important factor in the dispersal of plants. Fruits are favorable foods for many species of birds, and birds transport the fruit's seeds to another locality for germination and establishment. The seeds of juicy fruits (e.g., drupe, berry, hesperidium, pome, etaerio, cynarrhodium, etc.) are thus dispersed by birds in the way of endozoochoryl, since the juicy part of fruit or pericarp, especially mesocarp, is digested; but the seed is not, or can not be digested in the digestive tract of a bird (Figs. 1 and 3).
In the correlation of birds and juicy fruits, the pericarp has evolved in size, color, taste, etc. to be eaten by birds, and the seed coat, or shell (endocarp) of drupe, may have evolved in hardness not to be digested (Fig. 4). This hypothesis of the hardening of seed coat may be supported by the data of germination in nursing practices. Seeds of juicy fruits germinate generally in the next spring of sowing (Table 1). To soften the hard coat for rapid germination, we use knife, enzyme of bacteria, sulfuric acid, hydrogen peroxide, boiling water, etc; or we pick young fruits with greenish epicarp and uncompletely hardened seed coat (Fig. 5), and sow seeds without pericarp immediately after picking.
Fruit-eating birds soften the hard coat, as we do in nurseries. It is pointed out that the hardened coat of seeds of juicy fruits is not convenient for tree nursing but indispensable for ornithochoryl.