lo July. 1911-] Seeds and Seeding. 473 



seed coat. In many seeds it is eagerly absorbed by the seed coat itself, 

 -especially those with a mucilaginous envelope, as flax. Frequently there 

 are special absorbative systems developed in connexion with these apertures. 

 If the seed coat is not very thick or the integuments not very hard, the 

 moisture gradually finds its way to the embryo by osmosis. The absorp- 

 tion of water by the embryo, or, in some cases, the endosperm, leads to an 

 increase of size and a consequent rupture of the .seed coat. ^Vhere the latter 

 is thick and hard, it usually has some soft portion through which the 

 ■embryo emerges, as in the ccxroanut and sugar-cane. The radicle, being 

 situated in close proximity to the micropyle, is usually the first to emerge; 

 but in many monccotyledonous seeds the cotyledon is the first to appear. 



The seed coat is often a hindrance to germination. This is especially .so 

 with many leguminous and drupaceous seeds. In the.se cases, soaking in 

 hot water, cracking, or mechanically injuiing the integum.ents in some way, 

 is adopted to assist the water in reaching the embryo. Germination then 

 takes place more readily. Many of the half-hardy seeds, as melons, are 

 sensitive to the presence of moisture, and depreciate quickly if stored in 

 damp places; while hard seeds, such as cannas, acacias, kennedias, goodias, 

 &c., will remain in the ground for months without apparent injury. Seeds 

 of our stone fruits are often stored in moist sand during the winter. This 

 permits time for the moisture to gradually rot the outer .shell, and gain 

 access to the kernel in time for spring sprouting. * 



According to Haberlandt, the minimum temperature for germination 

 lies between 32 and 40.64 F. in the case of wheat, oats, barley, and peas; 

 between 40.64 and 50.90 F. in the case of maize; between 50.90 and 

 60.08 F. in the case of pumpkins and tobacco; and between 60.08 and 

 65.3 F. in the case of melons and cucumbers. It will be .seen that the 

 half-hardy seeds require higher temperatures :ft>r germination, hence it is 

 inadvisable to sow them in the open when the ground is cold and wet. 

 Seeds will not germinate below 32 F. owing to water ireezing at that 

 point, and thus preventing its absorption by the tissues of the .seed. How- 

 ■ever, manv .seeds, such as the common annual meadowgrass {Poa annua) 

 and chickweed {A/sine media), will germinate at slightly above that 

 temperature. 



During the process of germination, care should be taken to enable the 

 seed to obtain a sufficiency of air, as respiration is particularly active at that 

 time. This applies especially to those seeds the reserve products ot which 

 are of a fatty or oily nature, as more oxygen is utilized in oxydizing the 

 fats and oils. It is of some importance, therefore, that the growers have a 

 knowledge of the conditions demanded of different kinds of seeds. 



Since good germination is best effected in some friable or granular 

 medium, and is the result of growth processes brought about by the action 

 of warmth, moisture, and air in proportions suited to the special require- 

 ments of the seed, it is manifest that if these elements varv to a great 

 ■extent, or are continuously deficient, or in excess, the conditions will be 

 in such degree unfavourable, an<l will militate against the best results. In 

 field practice, the conditions often vary greatly and, when unfavoural>le. 

 the weaker .seeds fail. H<'nre, freer sowings should be made at certain 

 seasons, or when the conditions promise to be unfavourable. 



Under laboratory conditions, or in forcing frames or houses, where con- 

 ditions can Ije controlled to a nicety, seeds usuallv show a higher \italitv 

 test as against the viability {i.e., powers to grow) test in the open ground. 

 Although the seed tester is of great value in indicating the vitality of seeds, 

 or showing their germinating (]ualities, it dot\s not afford an accurate 

 criterion of tlicir viability, ov ability to grow under the less favourable 



