60 THE FRUIT. 



§ 3. OF GERMINATION. 



130. The embr}-o i3 the most important part of the seed. It is to the protec- 

 tion and nom-ishment of this alone, that all other parts of the seed, and even of 

 tlie Avhole plant, are subsersuent, and if this be injured or destroyed, the ultimate 

 object of the whole vegetable economy would seem to be defeated. 



a. Germination is a term denoting the first stages of \4tal 

 action in the seed; the process is briefly described as follows : 



131. When the seed is planted in a moist soil, at a moderate 

 temperature, the integuments gradually absorb water, soften, 

 and expand. The water is decomposed, its oxygen combines 

 with the carbon of the starch which had been stored up in the 

 tissues, carbonic acid is evolved, and the starch, at lengh con- 

 verted into sugar for the nourishment of the embryo, wliich now 

 begins to dilate and develope its parts. Soon the mtegnments 

 burst, the radicle descends, seeking the damp and dark bosom 

 of the earth, and the plumule arises, with expanding leaves, to 

 the air and the light.* (See Fig. 19, explanations.) 



132. As to the cotyledons, they either remain under ground at 

 the centre of motion, as in all Monocotyledonous plants and in 

 the oak, or, as in ahiiost all Dicotyledonous plants, they arise 

 above the surface with the ascending axis, become green, and 

 perform the functions of digestion and respiration, like leaves, 

 for the nourishment of the young plant; 



133. The conditions requisite for the germination of tlie seed 

 are heat, moisture, oxygen, and darkness. 



a. Heat is a i-equisite condition of all vital actions, as Avell in the sprouting of a 

 seed as in the hatching of an egg, and if it be not supplied from a source "«atMn, 



* The phenomena of germinalion, in all its stages, may be observed in an interesting ex- 

 periment. Let a few seeds, as of the flax or the pea, be enveloped in a lock of cotton, float- 

 ing upon water in a bulb-glass. Li a few days, the plumule ascends in its genial air, while 

 the radicle shoots downwards in long silky fibres. 



Tlie ascent of the plumule in a direction contrary to gra\ity is a law in vegetation, as uni- 

 versal as the law of attraction in matter, and no less difficult to explain. From the two 

 following experiments, it would seem to result both from the influence of the light and the 

 law of gravitation. Professor Shultz planted some seeds of cabbage, mustard, and beans, in 

 moss, and so arranged them that the only light which they could receive was from a mirror, 

 reflecting the solar rays upwards ; they sent their stems downwards, and their roots upwards. 



Mr. Kniglit placed vessels, containing earth with germinating seeds,, upon the circumfer- 

 ence of a large horizontal wheel, which M'as kept constantly and rapidly revolving for seve- 

 ral days. The seeds grew, but instead of ascending perpendicularly, the axis of each plant 

 was inclined at an angle of 45°, or more, towards the centre of the wheel, in accordance with 

 the combined action of the centrifugal force of the wheel, and the attraction of the earth. 



