CONDITIONS OF GERMINATION. 287 



Phanerogamia founded upon the structure of the seed, exactly 

 corresponds with that formed according to the structure of the 

 stem ; that is, all Exogens are Dicotyledonous (with only a few 

 apparent exceptions) ; and all Endogens are Monocotyledonous. 

 Moreover, all the Acrogens, which have no regular method of 

 adding to the diameter of their stem, are destitute of the power 

 of forming true seeds ; the germs being, as it were, at once cast 

 upon the world, instead of being reared and cherished by parental 

 care. It has formerly been pointed out, that Exogens, Endo- 

 gens, and Acrogens, differ also in the distribution of the veins in 

 their leaves (. 229 32) ; and it may here be mentioned, that 

 they differ also in the number of parts of which the flower is 

 usually composed. Thus, in Exogens, the regular number of 

 stamens is either four or five, or a multiple of one of these num- 

 bers ; and that of the carpels is similar : whilst in Endogens, 

 the number of the same parts is three, or a multiple of it. The 

 number of the external or leafy parts of the flower follows the 

 same laws, as will be hereafter explained. 



444. The conditions requisite for the germination of the 

 seed, are warmth, moisture, and the presence of oxygen. The 

 process is also favoured by darkness. The influence of each 

 of these agents will be readily understood. No vital action can 

 go on without a certain amount of heat ; and, where this is not 

 produced within the being, it must be derived from without. 

 The germination of the seed is as much dependent upon warmth, 

 therefore, as the hatching of the egg of a bird ; though the 

 amount it requires is not nearly so great. Moisture is also evi- 

 dently required, for the conversion, into a fluid state, of the dry 

 nutriment, which has been previously stored up in the seed ; 

 and no change can commence, until this be supplied. The pre- 

 sence of oxygen is necessary, because the conversion of starch 

 into sugar requires (as formerly stated, . 283) that some of the 

 carbon of the former should be set free ; and this can only be 

 accomplished, by the union of it with oxygen, so as to form car- 

 bonic acid. This process is favoured by darkness, because light 

 has a tendency to produce the contrary change i\\e fixation of 

 the carbon within the structure (. 286). 



