20 SEEDS A?ilJ SEEJjLINGS 



17. Water. — Seeds are usually rather thy on issuing 

 from the fruit. Drj-ness makes the seed hardy. In 

 contact with water therefore, at the time of germination, 

 they often swell to two or three times their dry volume. 

 Actual growth in iilants, too, always requires much water. 



18. Warmth, — Moderate heat has a strong influence in 

 hastening gcnuination. For Indian Corn and Squash the 

 DKwt favorable temperature is given as about 81° Fahr. 

 A few exceptional seeds will sprout at the freezing point 

 of water. Thus seeds of a Maple have been germinated 

 Oii a block of ice, the rootlets penetrating to a deptli of 

 more than t^\■o inches into the dense, clear ice, in which 

 they melted out cylindrical cavities for themselves. Heat 

 for growth is here generated by the seedling itself. 



19. Oxygen is actively inhaled and coudiines \\'ith the 

 substances of the embryo. This oxidation furnishes energy 

 which appears in growth and in vital Jieat ; that is, in heat 

 in the seedling similar in all respects to the bodily warmtli 

 of animals. 



20. As a result of oxidatiim carbonic acid gas is formed 

 and exhaled. Tlie young plant thus l)reathcs in and out. 

 Respiration is common to all living things. But in plants 

 the in-take of the one gas and the out-going of the other 

 are slow, continuous, and inq)erceptible processes. 



21. The development of seedlings. — If one looks under 

 the White Oak in late autumn, he is likely to find that the 

 acorns have sprouted. Me will tlicn discover that many of 

 the nuts, if lying on proper surface, for instance on sliort- 

 cropped pasture sward, are already fast-bound to the earth, 

 the radich'S, or incipient roots, having penetrated tlie soil. 

 It appears, therefore, that seeds may germinate and attach 

 themselves without being covered up ; though a covering 

 of some sort, as sand, soil, or dead leaves, is advantageous, 

 and some fruits, or their carpels, are even jirovided with 

 meclianical contrivances for partially Inirying themselves. ^ 



22. Suppose that a seed lies thus, like the acorn, cleanly 

 upon the surface, and that it has been drenclied by rain 



1 See Fig. 279. 



