288 CONDITIONS OF GERMINATION. 



445. It is interesting to observe how all these conditions are 

 supplied, in the ordinary course of Nature, by the soil in which 

 the seed is dropped. If it be sown during the spring or summer, 

 it speedily begins to germinate ; but if it is deposited in the 

 autumn, it remains almost unchanged, until the winter has 

 passed, and the returning warmth of the air and earth arouses 

 it into activity. It is seldom that the soil is so completely 

 destitute of moisture, for any long time together, as not to be 

 able to excite seeds to germinate ; but their sprouting is well 

 known to be favoured by damp weather ; and if seeds, through 

 being put into the ground during a drought, remain undeveloped, 

 they are brought forwards very rapidly by a genial shower. A 

 porous soil is to be preferred, on account of the free admission of 

 air, which it gives to a germinating seed ; as well as for the 

 other processes of vegetation (. 178, 9). A stiff clay soil pre- 

 vents this necessary contact ; and thus impedes germination. 

 So complete a check, indeed, may be thus produced, that it has 

 been proposed to bury seeds in clay rammed hard, when it is 

 desired to convey them from one part of the world to another, 

 through very hot climates ; the high temperature of which 

 might destroy their vitality, if its influence were not partly pre- 

 vented, by the bad-conducting power of the mass, in which they 

 are thus enclosed. If seeds be buried very deep, even in a light 

 soil, the contact of oxygen will be sufficiently impeded to pre- 

 vent their germination ; and the bringing such seeds nearer to 

 the surface, will then have as much influence in causing them 

 to sprout, as the supply of either of the agents just mentioned, 

 which might have been previously deficient. 



446. The seeds of most Plants are endowed with a remark- 

 able power of preserving their vitality, for an almost unlimited 

 time ; if they are placed in circumstances, which neither call 

 their properties into active exercise, nor occasion the decay of 

 their structure. The conditions most favourable for this preser- 

 vation, will evidently be, a low or moderate temperature, dry- 

 ness of the surrounding medium, and the absence of oxygen. If 

 all these be supplied in the most favourable manner, there seems 

 no limit to the period, during which seeds may retain their vita- 



