158 VEGETABLE PHYSIOLOGY. 



After fertilization flowers rapidly lose their fresliiiess ; the corolla and stamens 

 wither and fall; the style dries up, together with the conducting tisaue which 

 filled it, and that portion of this tissue which abutted on the ovule disappears. 

 Soon the ovary, receiving the nourishment which was previously distributed to other 

 parts of the flower, increases, as do the ovules ; many of these become arrested by 

 the overwhelming development of the others, and the number arrested is often 

 constant ; sometimes also the septa disappear. Finally, the fertilized pistil becomes 

 more or less modified in form, volume, and consistency. 



Maturation. — This marks the period when the changes which take place in the 

 fruit, from fertilization till the dispersion of the seed, are completed. Those fruits 

 which remain foliaceous continue, like the leaves, to decompose carbonic acid and 

 disengage oxygen by day, whilst by night they absorb oxygen and disengage 

 carbonic acid. At maturity their tissue dries, their colour changes, their fibro- 

 vascular bundles separate, and dehiscence takes place. 



Those fruits which lose their foliaceous consistency and become fleshy respire 

 like the preceding until maturity; then the parenchyma is fully developed, its 

 watery contents are decomposed, and fixed in new combinations ; the cellulose loses 

 some of its carbon and hydrogen, and becomes starch; and the latter, by the 

 addition of water, is changed into sugar. Vegetable acids are the equivalents of starch 

 and oxygen ; to change these acids into sugar, all that is necessary is either that 

 the carbon assimilated by the plant shall take up their o'sjg&XL, or that water shall 

 be formed at the expense of the latter. In most fruits these acids are not entirely 

 converted into sugar, but enter into combination with alkaline bases, thus modifying 

 their acid flavour. The proportions of acid and sugar vary according to the nature 

 of the fruit. 



When maturation is complete, the fruit disengages carbonic acid formed at the 

 expense of the sugar, and the latter gradually disappears ; but the decomposing 

 fruit, by disengaging carbonic acid around it, materially contributes to the nourish- 

 ment of the young seed. At complete maturity the fruit breaks up, and the seed 

 thereupon commences an independent existence. 



Dissemination is the act by which the ripe seeds are scattered over the surface 

 of the earth. In capsular fruits the seeds are freed by the dehiscence of the 

 carpels ; in fleshy fruits they are retained longer. 



Nature has infinitely varied the methods tending to disseminate seeds : wind, 

 water, and frugivorous animals are the principal agents ; and man himself assists, 

 often unwittingly, by his labours or voyages, in the transport and multiplication of 

 seeds. 



Germination.— The agents in germination are water, air, heat, and darkness. 

 Seeds bui-ied for many centuries • in dry soil, preserved from the air and from 

 variations of atmospheric temperature, have been known to germinate and reproduce 

 their species, when placed under favourable conditions. 



Water softens the integuments, penetrates the tissue of the seed, and is 



' The statements supposed to prove this are not generally trustworthy. — Ed. 



