LIFE OF PLANTS. 257 



Landwirthschaft.) The peculiar power of plants seems even 

 to be increased by this long keeping of their seeds, apparent- 

 ly because, by the drying up of the albuminous substance 

 and of the cotyledons, the constituent parts become more 

 concentrated and powerful. We hence choose old seeds of 

 melons, for the purpose of obtaining a rich crop of the best 

 flavoured fruit. Old Lint seed also gives commonly the 

 finest and best Flax. 



It is a further consequence of the different varieties which 

 the internal power of seeds exhibits, that many seeds germi- 

 nate very early, and others very late ; for we cannot find a 

 sufficient foundation for this difference, either in the structure 

 or in the apparent composition of the parts of the seed. 

 While the Umbellatae, Rosaceae, and Proteacese, often do not 

 appear till after two years, most of the Grasses, Cruciform, 

 and leguminous plants, on the contrary, germinate in a few 

 days. 



385. 



There is also a series of chemical changes, connected with 

 the germ, by means of which, as a sort of conditional causes, 

 the vital power of the germ is awakened. In the first 

 place, the seed attracts carbonic acid water through its 

 umbilicus, by which means a swelling of the albuminous 

 substance or of the cotyledons takes place, and an evident 

 effervescence is begun. During this latter operation, carbo- 

 nic acid gas is disengaged, and hydrogen is in part set free. 

 The external heat, the regulated influence of the light of the 

 sun, and the oxygen of the atmosphere, are the stimuli which 

 now awaken the life of the germ, and enable it to make use 

 of its proper nourishment, the carbonic acid water impreg- 

 nated with azote, for its full evolution. 



If the embryon remains still undeveloped in the seed, 

 more arrangements and preparations must be had recourse to, 

 before it will completely unfold itself. In many of the lower 

 plants, the necessity of these preparations consists in this, 

 that the awakening life, directed by no fixed original type, 

 produces fluctuating forms, which have often no resemblance 



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