284 PHYSIOLOGICAL BOTANY. PART II. 



(285.) Action of Moist tire. It has been found that 

 the quantity of water absorbed by seeds varies in pro- 

 portion to their bulk, and that all seeds absorb very 

 nearly a weight of water equal to their own. If a co- 

 loured liquid be used, it will be found to traverse the 

 substance of the seed cover (jparMMferm) until it col- 

 lects in the cellular tissue near the extremity of the 

 radicle. From this spot it is imbibed by the radicle, and 

 penetrates into the cotyledons of dicotyledonous plants, 

 along the minute and ramifying veins which traverse 

 tin-in. The chief use of the imbibed water appears to 

 be, to dissolve whatever materials have been prepared in 

 the seed for the nourishment of the embryo, and to 

 convey them into its substance. Where the cotyledons 

 are learlike and not fleshy, they contain very little nutri- 

 ment ; and if there is no free albumen, the cotyledons 

 themselves are furnished with stomata,,, immediately ex- 

 pand, and begin to elaborate nutriment by decomposing 

 carbonic acid. When the alburnum is free and surrounds 

 the cotyledons, it must in some way be absorbed by 

 their surface, though it is difficult to explain how. The 

 process bears a striking analogy to the suckling of the 

 young in animals. Seeds will not germinate in boiled 

 or distilled water, from which the oxygen has been ex- 

 pelled; and if they are placed in an atmosphere of hydro- 

 gen, azote, carbonic acid, or any pas which contains no 

 portion of oxygen, they are equally incapable of ger- 

 minating. They succeed best in a mixture of one part 

 oxygen with three of azote, and this is not very far 

 removed from the proportion in which these gases are 

 united in the atmosphere. Where the oxygen is in 

 larger quantity it over-stimulates the seed. 



(286.) Action of Oxygen. One use of oxygen in ger- 

 mination is to unite with the superfluous carbon which 

 has been prepared during the process of maturation for 

 the better preservation of the seed : thus it appears that 

 the first step in the new process is to undo the last by 

 which the maturation was completed. Consequently it is 



