ON PROPAGATION BY SEED. 207 



moisture prevents the germination of seeds, though every other requi- 

 site 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. The 

 presence of air and warmth are likewise necessary to the growth of 

 seeds. That the want of air has an effect in preventing the germina- 

 tion 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 communication 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 propor- 

 tionately larger quantity of water, the seeds will find in the air which 

 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. 



Process of Germination. If the husks are hard or impenetrable, 

 germination proceeds slowly. Various means have been adopted 

 to hasten the growth of acacias and other hard seeds. Steeping 

 in hot or boiling water has hastened the process ; but it is safer 

 to cut or file through the hard shell at one spot. From this spot 

 the seed imbibes the requisite quantity of air and moisture, the 

 radicle is quickly developed, and, with the help of the swollen tissue 

 within it, bursts the sutures of the husk. In this way many hard- 

 shelled seeds of monocotyledonous and dicotyledonous plants, such 

 as canna, paeonia, acacia, abrus, erythrina, cassia, schotia, guilandina, 

 adenanthera, bauhinia, and caesalpinia, have been made to ger- 

 minate in a short time, mostly in from ten to twenty days. If the 

 seeds be old, they should, after cutting, be laid for a few days in luke- 

 warm rain-water, and, if they have any life remaining, this will stimu- 

 late it. Something similar also takes place with seeds which, besides 

 the testa, or husk, are also enclosed in a pericarpium, or outer-cover- 

 ing. They lie either in fours, at the bottom of a dry hollow cup, as 

 in the labiatae and boragineae ; or they are single, or several, surrounded 

 with a thick fleshy cup, as in many species of the rosaceae ; or single, or 

 in twos, covered with a dry cup, as in compositae, umbelliferae, and their 

 allied species. Lastly, in the gramineae, we find them only surrounded 

 with the pericarpium, as true caryopses. Many of these germinate as 

 easily as naked seeds ; but this depends, in some measure, on the 

 capacity or incapacity of the husk to absorb water in a natural state. 

 We find seeds hard and stony only among the rosaceae, as in rosa, 

 prunus, cotoneaster, mespilus, crataegus, &c., and these require 

 cutting or filing, if intended to germinate quickly. The remainder 

 are divided, according to their formation, into two groups ; those pos- 

 sessing albumen, in which the embryo lies, and those that do not. 

 This division is useful, for the cotyledons always imbibe the water first 



