240 



ON PROPAGATION BY SEED. 



The seeds of the cultivated varieties of cabbage, peas, wheat, oats, Sec. it m 

 well known, produce plants in all respects like their parents, or in horticul- 

 tural language " come true." The seeds of trees, however, are not so much to 

 be depended on, as those of herbaceous plants, and especially of annuals, in a 

 high state of culture ; for a kernel out of the same apple which produced the 

 Ribstone pippin produced another tree, the fruit of which proved little better 

 than a crab. From these facts we consider it safe for the gardener to adopt it 

 as a principle, that the seeds of trees, as well as of herbaceous plants, will 

 not only reproduce the species, but, to a considerable extent, also the variety ; 

 though we cannot depend on this mode for. reproducing the variety, with 

 the same certainty as we can on propagation by division. 



§ 1. On propagation hy seed. 



552. The seed as we have seen (132), is of a mucilaginous consistency 

 when young, and it becomes more or less solid when matured. Before 

 germination can take place, the solid part of the seed must be rendered 

 again mucilaginous, and soluble in water ; and this is effected by the mois- 

 ture and heat of the soil, and the ox3^gen of the atmosphere. The absence 

 of light, or at least, of much light, is also favourable to germination, but 

 not essential to it ; for though, when seeds are sown, they are generally 

 covered in proportion to their size, in order to maintain an equal degree of 

 moisture, and to keep them in darkness, we also sow the smaller seeds, such 

 as those of ferns and heaths, on the surface, and maintain the requisite 

 moisture by means of a close covering of glass, only moderating the light by 

 placing them in the shade. That the want of moisture prevents the germina- 

 tion of seeds, though every other requisite should be present, is known to 

 every gardener ; and indeed, were it otherwise, it would be next to impossible 

 to preserve seeds from one season to another, since, though it is in our power 

 to keep them dry, it is scarcely practicable to prevent the access of air and 

 heat. That the want of air has an effect in preventing the germination of seeds 

 is proved by the following experiment. If a number of seeds be put in a 

 bottle with from ten to twenty times their bulk of water, and all communi- 

 cation with the surrounding atmosphere be cut off, so that the water may 

 not absorb any oxygen from it, the seeds will not germinate, though placed 

 in a temperature suitable for germination ; but if the same experiment be 

 repeated with a proportionately larger quantity of water, the seeds will find in 

 the air wliich it contains sufficient oxygen to enable them to germinate. 

 (Gard. Mag. for 1841, p. 482). That seeds will not germinate without 

 the presence of a certain degree of heat, is rendered evident by the fact of 

 self-sown seeds lying in the soil all the winter, and only vegetating when 

 the temperature becomes sufficiently high in the spring. 



553. Process of germination. The first change which takes place in 

 the germinating seed is seen immediately after the absorption of water, 

 when its substance becomes softer, often assumes a greenish tint, and tastes 

 sweetish. After this a lengthening of the radicle takes place, which 

 receives its nourishment from the cotyledons, or the albumen. It then 

 penetrates the testa or husk, through the micropylus, (an exceedinlgy 

 small hole in the husk of the seed, which corresponds with the point of the 

 radicle,) and ruptures it at this spot, so that the embryo now bursts forth. 

 The young plant is then nourished by the aliment laid up in the cotyledons, 

 or in the albumen of the seed, till the root begins to branch. Hence, it 



