256 



PHYTONOMY. 



thereby its transition to the true cotyledons becomes evident. 

 According to the observations of L. C. Treviranus, the thick- 

 ened cotyledonous termination of the Ruppia has the struc- 

 ture, and supplies the place of the albuminous substance ; 

 (Von der Entwickelung des Embryo.) 



In most of these albuminous plants, the cotyledonous body 

 IS first formed along with the germ. The Palms, for instance, 

 the Liliaceae, Junceae, and Sarmentaceae, send out from the 

 seed, along with the germ, a horizontal thread, which be- 

 comes thickened into a tubercle, and from which the root 

 proceeds downwards, and the plant upwards. A great many 

 families of plants retain the thickened fluid of the germ, as 

 albuminous substance, and yet the embryon is evolved with 

 its cotyledons. We observe this in the Umbellatae, Polygo- 

 neae, Nyctaginae, as well as in the Caryophylleas, in which 

 the albuminous substance remains in the middle, and the em- 

 bryon is placed around it. In plants of the higher orders, 

 however, it commonly happens that the evolution of the em- 

 bryon with its cotyledons is performed so much at the ex- 

 pense of the albuminous substance, that this substance is 

 either entirely consumed, and becomes one with the chorion^ 

 or there remains only a small trace of it. 



384. 



Although the chemical changes in the germ are of very 

 high moment, yet this process cannot otherwise be funda- 

 mentally explained but in a dynamical way. 



The object of first importance in germs is their vital acti- 

 vity ; and this in many plants dies so speedily, that acorns 

 and coff'ee-beans cannot be preserved above a few months, 

 without losing their power of germinating. On the other 

 hand, this power is retained in many other seeds for an ama- 

 zing length of time, especially when light and air are ex- 

 cluded ; and it is from this cause that we must account for 

 the otherwise incomprehensible phenomenon, that the bottom 

 of dried pools, or earth which has been stirred to a great 

 depth, produces plants, which do not make their appearance 

 for many miles round ; (Thaer, Grundsaze der rationellen 



