604 



COTYLEDONS. 



its lower end bores deeply into the mud. Even a layer of water half a metre deep 

 is pierced by it with such force that it remains standing upright in the mud 

 beneath. After a few days the pericarp, with the cotyledon inside, is also de- 

 tached. At the upper end of the fallen hypocotyl the bud which was formerly 

 covered over by the tubular cotyledon is now to be seen. The four small green 

 scale-leaves of this bud only increase slightly in length; but immediately, from 

 the shoot arising from it, large elliptical shiny green leaves are developed which 

 become active as foliage; whilst from the lower end of the hypocotyl which has 

 bored into the mud, as well as from the epicotyl itself, roots arise which are at 

 once the means of fixing the plant in the muddy shore, and of conducting food- 

 salts to it. In the neighbourhood of old mangrove trees, dozens of these young 

 plants may be seen, which have fallen and bored their way into the mud; and on 

 the shoots produced from their upper ends sometimes only scale-leaves, and some- 

 times foliage-leaves are developed. The illustration opposite, taken from a sketch 

 near Goa, on the coast of Bombay, drawn from nature by Ransonnet, shows all 

 this very clearly. 



The second form of cotyledon to be brought forward is that which occurs in 

 grasses, and is called by botanists the scutellum. Although variously modified, 

 it is in the main developed similarly* in the many thousands of different species. 

 The small embryo of the grass is in lateral contact with one end of the large starchy 

 reserve-tissue, by means of its cotyledon, as shown in the grain of wheat chosen 

 as type (see figs. 141 4 and 141 5 ). The free edges of the cotyledon arch over the 

 embryo bud, sometimes actually curling round it, forming a sheath-like envelope. 

 Below, the cotyledon is continued into a sac which incloses the radicle of the 

 embryo. When the materials are conveyed from the reserve-tissue to the hypo- 

 cotyl, radicle, and embryo-bud, by means of the absorbent cells of the cotyledon 

 described on p. 600, these portions quickly increase in length. The radicle pierces 

 the sac-like envelope, penetrates into the ground, and unites by abundant root- 

 hairs with the particles of the soil. The bud also elongates and the leaves grow up 

 into the light from the sheath-like envelope of the cotyledon. The lower leaves 

 are usually scale-leaves without green blades, but the leaves following these all 

 exhibit large green laminae which function as foliage. The starch of the reservoir 

 is soon completely consumed in the rapid growth of the embryo. As soon as this 

 has happened the cotyledon has no further task to fulfil, it shrivels and perishes, 

 but the young grass-plant with its roots and its green foliage-leaves is now in 

 a position to manufacture for itself the substances necessary for its further 

 construction. 



The third form of cotyledon is shown in the embryos of sedges and rushes, 

 of irises, snowdrops, narcissus, aloes, and butcher's-broom, of flowering rushes, 

 bananas, and palms, and numerous other plants belonging to the class of monocoty- 

 ledons. In all these plants the embryo is embedded in the reserve-tissue of the 

 seed, and the cotyledon proceeding from the hypocotyl forms a sheath surrounding 

 the bud situated upon it. The cotyledon is provided with absorbent cells only at 



