CHAP. VI. FUNCTION OF REPRODUCTION. 283 



usual way. This period bears some analogy to that of 

 suckling in the Mammalia, or still more strikingly to 

 that of incubation in birds. 



(284.) Stimulants to Germination. There are 

 three requisites to germination, either of which being 

 wanting the process will not take place. These are 

 moisture, oxygen, and a certain elevation of temper- 

 ature. When the conditions requisite for the germina- 

 ation of a seed are satisfied, it imbibes moisture through 

 its integuments, the embryo swells, and the radicle is 

 protruded and tends downwards. The plumule or 

 terminal bud then expands and rises upwards ; the 

 albumen, either free or contained in the cotyledons, is 

 soon exhausted ; the young plant takes firm hold on the 

 ground and commences its independent existence. 



Although the period which elapses between the time 

 when seeds are sown and when they first begin to ger- 

 minate is very different even in the same species, ac- 

 cording to the external conditions under which they are 

 placed, yet if different seeds are subjected to precisely 

 the same influences, we find a still more remarkable dif- 

 ference between the periods which elapse before they se- 

 verally germinate. The following list exhibits the result 

 of some experiments made at the Geneva garden, on 

 seeds similarly watered and exposed to a common tem- 

 perature of 95 R. It was ascertained that about half 

 the species of the following families germinated after 

 the lapse of the number of days here mentioned, viz : 

 Days. 



9- Amaranthaceae. 



10. Cruciferae. 



11. Cariophyllaceae, Malvaceae. 



12. Composite, Convolvulaceae. 



13. Polygoneae. 



14. Leguminosae, Valerianeae. 



15. Graminese, Labiatse, Solaneae. 

 20. Ranunculacese. 



22. Onagrariae. 



23. Umbelliferse. 



