G3 



CASSELL'S POPULAH GAEDENIXG. 



Light It is generally telieved that darknesa 



assists germination, and that light retards it, but 

 ■whether the presence or absence of light alone affects 

 the germinative process either one way or the other 

 has not yet been clearly shown. Various and 

 numerous experiments have been made to test 

 whether the action of light on germinating seeds is 

 for their good, and the general conclusion thus 

 arrived at appears to favour the view that it is not. 

 If this were not so, it might be asked, why cover 

 seeds with earth, or, if fine, place them in a darkened 

 position ? The answer to this question must be, 

 that seeds are covered, not so much to exclude light 

 as to keep them uniformly moist, and to prevent 

 irregularities in temperature. For all seeds sown 

 out of doors we know that a covering of soil, varying 

 in depth with the size of the seeds, is necessary, and 

 the same is understood to apply for seeds under 

 glass, unless they be very small. Yet we know that 

 moisturp, and a certain degree of heat, along with 

 atmospheric influences, are sufficient to cause any. 

 seed to germinate, whether placed in darkness or in 

 bright light. 



F;requent proofs of this occur in the propagating 

 department at Kew, where, as is stated above, 

 many kinds of seeds are sown annually. In 

 addition to this, the discussion on the question of 

 darkness for seeds, which took place in the horti- 

 cultural papers some time ago, led to various 

 experiments at, Kew to test how far light affected 

 the process of gerinination. Seeds were sown on the 

 surface of soil, on cocoa-nut fibre, and in water in a 

 bell-glass, and to prevent evaporation squares of 

 glass were placed over the seeds in such a way as 

 would admit sufficient air without excluding any 

 light. The result of these experiments appeared to 

 show that light did not prevent, nor appreciably 

 interfere with, germination, the seeds starting into 

 growth at about the same time as those which were 

 covered with soil in the usual way. Before it can 

 be satisfactorily proved that these conclusions were 

 safe more experiments will be necessary, but so far 

 as we have gone the evidence gathered favours 

 the opinion that light alone does not interfere with 

 the germiuation of seeds. Every gardener knows 

 how freely the 'Smallest seeds will vegetate if sown 

 on the surfacfe of soil, covered with a pane of glass 

 and placed on a shelf near the light ; seeds of such 

 plants as Gloxinia, Gesnera, Primula, Calceolaria, 

 Begonia, and Bertolonia are commonly sown in this 

 way. Orchids, too, are raised from seeds scattered 

 upon the surface of living Sphagnum moss, where 

 darkness is out of the question. If fine Seeds are 

 not injured by light, may we not conclude that larger 

 ones are equally unaffected by it ? Experiments like 

 the above prove that such is most probably the case. 



As already stated, seeds are covered with soil to-i 

 afford them the necessary moisture and warmth; 

 it is also necessary, at least in the case of large seeds, 

 to enable the root to take firm hold of the soil, by 

 presenting an opposing force to the pressure of the 

 root as it prolongs itself and pushes its point into 

 the ground. For these reasons, irrespective of the 

 question of light, a covering of soil is beneficial to aU 

 but the smallest seeds. Various . scales have beeiL 

 given of the different depths at which seeds of 

 different sizes should be sown, but the best we can 

 suggest, and the one found least likely to mis- 

 lead, is that the thickness of the covering of soil 

 for seeds should not exceed their own diameter. For 

 seeds sown out of doors it is perhaps better to sow a 

 little deeper, for the sake of a proper degree of 

 moisture, and to prevent their being eaten by birds, 

 &c. Under glass this rule can never be far wrong- 

 Deep sowing is often unfavourable to germination,, 

 rather because of the exclusion of a due amount of 

 air, than through darkness or the absence of any 

 other condition. Numerous instances of this are not 

 imf requently recorded ; as, for instance, when land 

 has been cleaxed of trees, or when the earth has- 

 been turned over to any depth, a new vegetation 

 springs up, which is often composed of plants- 

 unknown in the near neighbourhood of the newly- 

 cleared land, and must * therefore have sprung from 

 seeds buried in the earth at too great a depth to- 

 permit vegetation. Seeds thus buried retain their 

 vitaHty for a very long period. At Kew it some- 

 times happens that seeds which on first sowing were 

 buried too low down in the soil have remained 

 dormant for a long while, but on bringing them 

 nearer the surface they generally germinate soon. 



Dr. Lindley mentions an instance of how seeds of 

 Flax were affected by deep sowing : " The injurious- 

 ness of covering seed with too much earth arises 

 less from the superincumbent pressure of the soil 

 than from the exclusion of atmospheric air,, which is 

 quite indispensable to germination. The seed of 

 the common Flax comes up at different periods, 

 according as it is planted in one, two, or three inches 

 depth of soil ; if it be sown four inches below the 

 surface it will not come up at all. Not that air does 

 not penetrate to this depth in the soil, but the- 

 quantity of air wiU very much depend on the looser 

 or denser character of the soil." 



Soil. — For all seeds of any size and the vegetative 

 power of which is strong and quick-acting, the soil 

 most suitable is such as the plants would thrive best 

 in when large. It is always best to use a finely- 

 sifted soil, at least for deKoate-rooted seedlings ; for 

 the smallest seed the mixture ought always to' be- 

 sifted through a sieve with a quarter-inch mesh., 



