io8 



winter. The actual disturbances are found to be the lack of external con- 

 ditions necessary for germination. Besides moisture and warmth there be- 

 long here the unimpeded supply of oxygen and the observance of the time 

 when the seed is capable of re-acting. 



The time within which the seed responds to the action of the external 

 conditions necessary for germination by a normal transmutation of the re- 

 serve substances and the development of the embryo varies greatly, for the 

 different families and species, even for individuals of the same variety. It 

 is well-known that seeds of willows, poplars and elms must be sown im- 

 mediately after harvesting, since they lose their power of germination after 

 a few days or weeks, while cucumbers and melons often give stronger, more 

 fertile plants, if the seeds have been kept for a year. To be sure, the seeds 

 of many of our fruit and forest trees usually germinate after one or more 

 years, but the number of the slow growing, weakened specimens increases 

 with the age of the seed. 



Oxygen should be considered the most important factor next to water, 

 necessary for swelling. For germination the seeds never need as much water 

 as their substance can take up ; the vegetative activity of the seedling begins 

 before this time\ If in the beginning there is a scarcity of water 

 which can be taken up endosmotically, the seed also takes water up hydro- 

 scopically from the atmosphere'-. Water vapor also condenses on the 

 outer surface ; in fact, after the manner of all porous bodies, it condenses 

 also hydrogen, nitrogen oxygen and other gases. Deherain and Landrin-' 

 found that the swollen seeds take up comparatively more oxygen than 

 nitrogen from the atmosphere so that more nitrogen remains in the en- 

 closed space. After three days the seed begins to give off carbon dioxid and 

 this increases so fast that soon more carbon dioxid is present than the oxygen 

 enclosed in the volume of the air would warrant, the oxygen has gradually 

 disappeared. The excessive production of carbon dioxid is therefore to be 

 considered as a product of the processes of oxidation of the inner burning, 

 beginning in the seeds. 



These authors pictured to themselves the beginning of the chemical 

 actions in the seed in such a way that the rapid condensation of the gas de- 

 termined at first for the various seeds will necessarily free the latent warmth 

 of the gas and this warmth sufficiently increases the temperature of the en- 

 closed oxygen so that oxidation can begin. With this is given the impetus for 

 the normal solution of the reserve substance of the seed ; the heat, freed by 

 oxidation, favors these processes more and more and they become evident 

 externally by the production of carbon dioxid. 



1 Jahresb. f. Agrikulturohemie, 18.S0, p. 213. 



- Hoffmann, R., in the Jahresbericht der agrikulturcheniischen Untersuchung- 

 station in Bohmen, 1864, p. 6. :ind Haberlandt, F., in Zeitschrift fiir deutsclie I^and- 

 wirte, 1863, p. 355. Both works may be found in abstract in the Jahresb. f. Agrikul- 

 turohemie, Jahrg. VII. 1864, pp. 108 and 111. 



H Compt. rend. 1874, Vol. LXXVIII, p. 1488, cit. in Biedermann's Centralbl. f. 

 Agrikulturchemie, 1874, II, p. 185. 



