ON THE PHYSIOLOGY OF PLANT?. 99 



however, is at all times bad, especially for seedlings, as it excites the 

 growth too rapidly, and disease is the consequence. Too much 

 moisture, again, will make the contents of the seed too poor, aud the 

 vessels of the embryo will be gorged, and disease is in this case the 

 consequence. Light, says Professor Rennie, retards the germination 

 of seeds ; for though they may have a due supply of oxygen and 

 water, they will not grow, at least healthily, unless in the dark. 

 The reason is, he says, that light causes the oxygen, which is indis- 

 pensable to their growth, to be carried off, and fixes in them the 

 carbonic acid gas, which is as yet improper food for the embryo 

 plant. It is plain then to be seen that care must be taken not to 

 give seeds, when first placed in the ground, too much water, or to 

 place them in such a heat as shall draw up the plant too quickly, 

 and so cause them to grow up weak ; nor to place them in so light a 

 situation that, instead of their growing and thriving as we hope, they 

 should be poisoned by mistaken kindness, and consequently never 

 make their appearance above ground. It has been proved by expe- 

 riment that seeds gathered before they are quite ripe germinate 

 sooner than very ripe ones, because the nutrient matter is less 

 hard ; but it does not follow that they will by that means produce 

 the best plants. 



And now we arrive at the time necessary for the young plants to 

 be pricked out, which, by the bye, it must be remembered is not 

 suitable in all cases, as some such, as Larkspurs, should, if required 

 in their best .bloom, remain. where sown, either in pots or in the 

 borders. If a Balsam is pricked out for flowering in the beds, it 

 almost invariably flags and droops; but it is in the end of much 

 service to the plant, as otherwise it would, if in a good soil and well 

 watered, send up so much sap, that the light could not readily 

 deprive it of its oxygen and water, and so it would push out more 

 leaves to carry off the superabundance, whilst the pulp would not 

 contain enough carbon to produce flowers ; hence the check given to 

 the Balsam, as in many other plants, prevents that superabundance 

 of sap, and causes the leaf pulp to thicken, and so to produce enough 

 carbon for flowering. Another important thing is not to plant the 

 roots too deep, as they are by that means prevented from obtaining 

 air, which is very necessary for their growth. 



In transplanting, great cara fchoidd be :taken that the roots be in 



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