134 sap. 



pelling by transplantation a plant to expend all its accumulated sap in the 

 nourishment of its seed, instead of in the superabundant production of 

 foliage, a crop of seed may be procured, the plants produced by which will, 

 in a great measure, have the peculiar properties of the parent variety. 



253. By a series of progressive seed-savings upon the same plan, plants 

 will be at length obtained, in which the habits of the individual have 

 become as it were fixed, and capable of such exact reproduction by seed, as 

 to form an exception to the general rule ; as in Turnips, Radishes, &c. 



254. But if the least neglect occurs in taking the necessary precautions 

 (252) to ensure a uniform crop of seed, possessing the new fixed proper- 

 ties, the race becomes deteriorated, in proportion to the want of care that 

 has occurred, and loses its characters of individuality. 



255. In all varieties those seed may be expected to preserve their indi- 

 vidual characters most distinctly which have been the best nourished (243) ; 

 it is, consequently, those which should be selected in preference for raising 

 new plants, from which seed is to be saved. 



256. When seed are first ripened, their embryo is a mass of cellular sub- 

 stance, containing starch, fixed carbon, or other solid matter, in its cavities ; 

 and in this state it will remain until fitting circumstances occur to call it 

 into active life. 



257. These fitting circumstances are, a temperature above 32 Fahrenheit, 

 a moist medium, darkness, and exposure to air. 



258. It then absorbs the moisture of the medium in which it lies, inhales 

 oxygen (278), and undergoes certain chemical changes ; its vital powers 

 cause it to ascend by one extremity for the purpose of finding light, and 

 of decomposing its carbonic acid (279), by parting with its accumulated 

 oxygen, and to descend by the other extremity for the purpose of finding 

 a constant supply of crude nutriment. 



259. Unless these conditions are maintained, seed cannot germinate; 

 and, consequently, an exposure to light is fatal to their embryo, because 

 (278) oxygen will not be absorbed in sufficient quantity to stimulate the 

 vital powers of the embryo into action, for the purpose of parting with it 

 again, by the decomposition of the carbonic acid that has been formed dur- 

 ing its accumulation. 



X. Sap. 



260. The fluid matter which is absorbed either from the earth or from 

 the air is called sap. 



261. When it first enters a plant it consists of water holding certain 

 principles, especially carbonic acid, in solution. 



262. These principles chiefly consist of animal or vegetable matter in a 

 state of decomposition, and are energetic in proportion to their solubility, 

 or tendency to form carbonic acid by combining with the oxygen of the air. 



263. Sap soon afterward acquires the nature of mucilage or sugar, and 

 subsequently becomes still farther altered by the admixture of such soluble 

 matter as it receives in passing in its route through the alburnum or newly 

 formed woody tissue (65). 



264. When it reaches the vicinity of the leaves it is attracted into them, 

 and there, having been exposed to light and air, is converted into the secre- 

 tions peculiar to the species. 





