24.4 



ON PROPAGATION BY SEED. 



the Horticultural Society, some years ago, by Mr. Palmer of Bromley, Kent. 

 Messrs. Edwards and Colin found that wheat, barley, and rye could germinate 

 between 44° and 45" ; that they were killed by remaining three days in water 

 at the temperature of OS** ; that in sand and earth, at 104^, they lived for a 

 considerable time ; but that at 113° most of them perished ; and that at 122° 

 all of them perished ; but it was found that a higher temperature could be 

 borne by these and other seeds for a shorter time. At 143°, in vapour, wheat, 

 barley, kidney-beans, and flax retained their vitality for a quarter of an 

 hour ; in dry air these seeds sustained no injury at 167°; but in vapour, at 

 this temperature, they all perished. Dr. Lindley mentions the very remark- 

 able case of the germination of the seeds of a raspberry, which had been 

 picked from a jar of jam, and which, consequently, must have been subjected 

 to the temperature of the boiling point of the syrup, which is 230°. 



560. The degree of cold which seeds will endure differs according to the species, 

 their native country, and their condition in respect to moisture. Dry seeds 

 stand so high a degree of cold, that even the lowest temperature of the frigid 

 zone does not injure them ; but if they have imbibed any moisture they freeze 

 according to the degree of growth which may have been excited, and the 

 degree of cold to which they had been accustomed in their native zone. 



561. Atmospheric air^ as we have seen (102), is as necessary to the ger- 

 mination of seeds as moisture and heat ; and this is the principal cause why 

 seeds buried to a certain depth in the soil do not vegetate. It also affords 

 a reason for having the surface of the soil, in which seeds are sown, porous, 

 and exposed to the action of the atmosphere, and to rain-water, which con- 

 tains more air than the water of wells. Hence the rapidity with which seeds 

 spring up in the open ground after the first warm spring showers. Hence, 

 also, the propriety of giving fresh air to hot-beds, and to hand and bellglasses 

 covering sown seeds, even though they have not come up. Old seeds are 

 found to germinate sooner in pure oxygen than in atmospheric air : doubtless, 

 because less efforts are required by the vital powers of the seed to assimilate 

 the oxygen with its carbon, so as to form carbonic acid. 



562. The influence of light on the germination of seeds has been already 

 alluded to (552). Bright light is found to be universally unfavourable ; 

 because it has a tendency to decompose carbonic acid, and fix carbon ; 

 whereas, as we have seen (553), the first step in the progress of germination 

 is to render carbon mucilaginous and soluble in water, so to change it into 

 carbonic acid. Light, therefore, ought to be excluded from all seeds which 

 it is wished should germinate freely. 



563. Accelerating the germination of seeds. In ordinary practice this is 

 chiefly effected by the application of a higher degree of heat, as by placing 

 pots of sown seeds in hot-beds, or by immersing seeds in tepid water, or by 

 cutting or paring nuts, or gently fermenting them in heaps of sawdust, as is 

 done with chestnuts, walnuts, acorns, almonds, &c., by the Paris nursery- 

 men. On a large scale, both in the field and the garden, the most common 

 resource is steeping in warm water for a few hours, which is found to bring 

 up the seeds of barley, turnips, beets, parsnips, onions, &c., when the soil in 

 which they are sown is very dry, much sooner than would otherwise bo the 

 case ; this is found to prevent them from becoming a prey to insects or birds. 

 The sowing of some seeds before they are perfectly ripe has also been found 

 to promote their early vegetation ; but the experience of gardeners in this 

 mode of acceleration is at present vcr^y limited. 



