GERMINATION. 127 



fruit. If the acid increases, tlie other principles diminisli. 

 If the other principles increase the acid diininishos. 



For these processes to <;;o on, an atmosphere c(tntain- 

 in<T oxvir<>n is necessary , showinj' that this active aixont is 

 required in these operaiions, and performs some necessary 

 otVice in the conversion of the crude material of green fruit 

 ipto the paliilahle ones of the rijtc. 



Skction 5. Germination. 



160. Bv germination uc understand the commoncoment of 

 the vital action which produces a development of the embryo 

 oftheseetl. The necessary conditions of germination are 

 the presence of water, heat and oxygen gas. The last is usu- 

 ally supplied hy the air. 



161. Germination cannot take place in the absence of any 

 one of these agents, and in ihe absence of water, no effect is 

 produced towards germination by the exposure to both of the 

 other agents. Wiih it they act promptly. The water enters 

 the seed by the hdum, and passes to the perisperm by the cha- 

 laza, from the perisperm to the embryo througli its point of 

 attachment. Tiiis is the direct course of the fluid through 

 appropriate vessels : but in some cases, as in the Beans and 

 Peas, it will ponetrate the testa and enter the embryo directly 

 through itssubslance, when the vesselsof the hilum are oijstruct- 

 ed, by being covered with waxorother substances impermeable 

 to water, but germination goes on much more tardy. In others 

 the obstruction of the vesstils jiroceeding from the hilum, pre- 

 vent germination entirely as in W heat, Oats, 6:c. This dif. 

 ference may very readily be imagined to arise from the fact, 

 that the wheat is not only covered by a testa, but also with 

 the pericarp, which is fitted to resist the action of external 

 agents, as other pericarps are ; wh.le the bean is covered only 

 by the testa, its pericarp having discharged its contents at 

 maturity. The wheat being deprived of its pericarp, germi- 

 nates ])romptly when its hilum is obstructed and the seed im- 

 mersed in water, as the testa is but a thin mucilaginous tissue. 



162. Seeds will not germinate in a vacuum, nor in anv 

 gas except oxygen ; nor in distilled or recently boiled water, 

 but by the presence of 0.3 of oxygen in any of these cases, 

 germination v. ill commence, 'i'he action of the oxygen seems 

 to he in combining with the carbon of the seed, and forming 

 carbonic acid ; producing as Raspail says, fermentation; a 

 part of the acid is thrown off, and a part no doubt elaborated 

 by the increa/.ing embryo. It has lieen recently proved by 



