"phy biologically considered. 483 



to injure the seed, and, at the same time, produce an equal 

 temperature. When circumstances permit, low houses, with 

 beds prepared for heating, particularly for early sowing, are 

 much to be recommended. If the seeds of tropical plants were 

 treated like those of our climate, they would, no doubt, absorb 

 moisture and oxygen ; but, for want of the necessary warmth 

 for promoting the change of matter (or vegetation), instead of 

 the process of assimilation, a fermenting process would take 

 place, which would destroy the seed. 



For this reason cold sowing late in autumn is to be avoided, 

 except for seeds difficult of germination. The middle of March 

 will do for beginning to sow the quickly growing sorts, namely, 

 the annuals, in dung-beds ; it is, however, better to delay it some 

 time longei', to prevent the plants growing too rank. It must 

 not be neglected to give air from time to time, even to the seed 

 which has not come up, in order that it may have sufficient 

 oxygen for its developement. 



How much a moderate degree of heat promotes germination, 

 the gardener may almost every day convince himself of; but any 

 one can observe, every year, how the seed sown in the open 

 ground after the first warm spring rains suddenly springs up, if 

 the ground has been sufficiently moist before. But this does not 

 seem to be occasioned by heat alone, as the same effi^ct may be 

 observed in temperate seed-beds, kept regularly warm and moist, 

 when, by removing the sashes, they are exposed to the influence 

 of the atmosphere and a gentle rain. A greater quantity of 

 oxygen seems then to be present in the rain-water and the air, 

 which, penetrating with the rain into the ground, excites the 

 seed to the greatest activity. 



The first change which takes place in the germinating seed 

 is seen immediately after the absorption of the water in the 

 cotyledons (or seed leaves), the substance of which becomes 

 softer, often assumes a greenish tint, and tastes sweetish. After 

 this a lengthening of the root takes place, which receives its 

 nourishment from the cotyledons. It then penetrates the husk, 

 through the micropylus (a very small hole in the husk of the 

 seed, which corresponds with the point of the root), and breaks 

 it at this spot, so that the embryo and cotyledons now burst 

 forth. The young plant is then nourished by the aliment laid 

 up in the cotyledons, till the root begins to branch. Hence it 

 often happens, that, when the cotyledons are destroyed by insects 

 or otherwise, the young plants are irretrievably lost. 



As soon as the husks become soft and tender, the seeds absorb 

 the surrounding moisture, and germinate in general, if they are 

 not too old, very quickly. If the husk is, on the contrary, hard, 

 and as in many cases stony, the moisture penetrates only through 

 the micropylus, and is communicated to the cotyledons by the 



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