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GARDEyERS- CHROMCLE 



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I A Lesson on Plant Physiology and the Plant in | 



I Relation to Its Environment | 



i Being One of a Series of Lessons of a Home Study Course on Garuening. Appearing Regularly in The Gardeners' Chronicle M 



I Under the Direction of ARTHUR SMITH | 



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THE germination of seeds is a very wonderful phenomenon 

 to watch, and by doing so some interesting facts may be 

 observed. Viable seeds will germinate on the surfac; of well 

 moistened soil or sand if we provide a damp atmosphere above 

 them by covering with a glass bell-jar or something similar, as 

 light does not hinder germination. 



After germination has commenced the seed-case is of no fur- 

 ther use. It has fulfilled its purpose, which is to protect the seed 

 from the time of its maturity until conditions arrive suitable for 

 germination ; henceforth it is a hindrance to germination in many 

 plants as it must be torn asunder by the expanding plantlet. If 

 we watch the germination of a squash or sitnilar seed through 

 the different stages we can discover that Nature has made a 

 special provision to help the plantlet in escaping from the seed- 

 case. Tlie first shoot from the germinating seed is called the 

 hypocotyl, which first grows downward no matter in what posi- 

 tion the seed is placed. It will curve in a semicircle if necessary 

 in order to bring its rounded point into the soil. Strictly speak- 

 ing, the hypocotyl is that portion of the^stem or axis which is 

 situate below the cotyledons of the embryo and which is above 

 the root. As the hypocotyl grows downward, a projection or 

 hook is forined on the side towards the seed ; this hook holds the 

 seed-case down while the seed-leaves (cotyledons), are pulled 

 out from it. Sometimes the point of the seed-case breaks, thus 

 permitting the hook to slip ofT ; also, if the seed happens to be 

 planted edgewise, or with the point downward, the hook often 

 fails to catch the seed-case, and therefore the plantlet emerges 

 from the soil without freeing itself from the seed-case and is 

 for a time hampered. This provision is peculiar to the pumpkin 

 family, to which squash, melons and cucumbers belong, although 

 other' provisions accomplishing the same end are found in a few 

 other families ; many plants are, however, considerably held back 

 by the seed-case during germination. Seeds of the pumpkin 

 family should be planted flatwise rather than edge, or endwise, 

 since' in this position they most readily free themselves from 

 their seed-cases. Lima beans are best planted edgewise with the 

 concave side downward. 



The best depth at which to plant seeds of different species 

 varies in a general way with their size, and the rule sometimes 

 given is that seeds should be covered with a thickness of soil 

 equal to four times their diameter. As above luentioned, the iirst 

 shoot from the seed called the hypocotyl. grows downward, but 

 if the seed is sufiicientlv covered, the point of the hypocotyl is 

 not always able to penetrate into the soil because the resistance 

 offered bv the latter is not only often greater than the pressure 

 offered bv the weight of the seed, but, what appears to be in this 

 connection more important, the larger the seed the larger is the 

 hypocotyl. and it obviously requires more force to push a large 

 root into the soil than it does a small one ; therefore a large seed 

 requires the additional weight of a thicker covering of soil so 

 as to afford sufficient additional leverage to enable the root to 

 grow downwards, otherwise the germinating embryo would be 

 entirely lifted out and from lack of moisture be unable to com- 

 plete the act of germination. It must, however, be admitted_ that 

 this latter event Is only likely to happen under conditions of bad 

 soil preparation so that the ground under the seed is hard and 



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The rule that the depth of planting is governed by the size of 

 the seed is, like most other rules, subject to exceptions, which 

 exceptions are connected with the special mode of germination 

 practised by different seeds. If we take a pea or a bean and 

 soak them in water so that the seed-case can be easily removed, 

 we shall find that they divide almost of themselves into halves 

 joined together at one point, and at the point of junction the 

 embryo can be easily seen. These two parts of a seed arc known 

 as cotyledons. 



Plants having two cotyledons form the very important class 

 known in botany as Dicotyledons ; while those known as Mono- 

 cotyledons have' but one cotyledon. There is also a class, which 

 includes conifers, in which the members have several cotyledons. 

 In some cases the cotyledons remain in the soil, and in others 

 they are lifted bodily into the air in the act of germination; it is 

 this distinction which has to be considered when covering large 

 seeds like the pea, bean, pumpkin, etc. In the case of the pea, 



the cotyledons remain in the soil, and this species will germinate 

 from a depth of five or six inches as it is only the pointed shoo': 

 which has to be forced through the covering soil. But with beans^ 

 pumpkins, and many others whose cotyledons must reach the 

 upper air before germination can be completed, it obviously re- 

 quires considerably greater force to push the more or less broad 

 cotyledons through the soil than it does a mere pointed shoot. 

 Therefore if seeds like beans, etc., are covered too deeply the 

 hypocotyl is often unable to lift the cotyledons to the surface and 

 the plantlet perishes. Frequently, too, the energy used by the 

 hypocotyl is sufficient to break off the cotyledons and the plantlet 

 emerges minus these appendages, in which case also it dies. Seeds 

 of the larger beans usually fail if covered to a depth of three 

 inches, especially if the soil is clayey, while those of the Castor 

 Bean, though very robust, can hardly lift their cotyledons through 

 one inch of soil. Wheat, corn, and other similar monocotyledons,, 

 will germinate through five inches of soil as their tiny, pointed 

 shoots readily insinuate themselves between the soil particles 

 and come to the surface with comparatively little expenditure of 

 energy ; it is not, however, necessary nor advisable to plant them 

 so deeply. 



As a rule the earlier germinations from a sowing of seed pro- 

 duce more vigorous plants than later ones. This is sometimes, 

 looked upon as one of Nature's methods for preserving the vigor 

 of species, as the stronger seedlings overtop the weaker ones and 

 crowd them out of existence. This should he remembered when 

 transplanting from a seed-bed and we should therefore reject 

 if possible plants from the later germinations. In all cases the 

 covering of soil over seeds should not be deeper than is abso- 

 lutely necessary because it is advisable to secure the completion 

 of germination in the shortest time possible. As previously men- 

 tioned, when a plantlet has used up the food supply in the seed 

 before germination is complete, it is liable to die, and in any 

 case it is likely to be weakened if it has to grow through an 

 excessive thickness of soil, even if it is possible for this to take 

 place. In respect to peas, for instance, while they will germinate 

 through five or six inches of soil covering, it is not advisable to 

 cover them to that depth in spite of the fact that it is necessary 

 to have the roots of peas as deeply placed in the ground as pos- 

 sible for the purpose of keeping the roots away from the (to them) 

 deleterious effects of hot weather. The latter is sometimes secured 

 by mulching, but a good method is to sow peas at the bottom of a 

 trench si.x inches deep and cover them with two inches of soil ; 

 then gradually fill in the trench as the peas grow. In all cases 

 seeds may be covered about a fourth deeper in a sandy soil than 

 in a clayey one. 



Very small seeds, celery, petunia, begonia, and such like, 

 should be scarcely covered at all. When seeds of this character 

 are .sown in pots or flats under artificial conditions, such as the 

 window of a room, in a greenhouse or frame, it is best to merely 

 press them into the surface of the soil and cover with a sheet 

 of glass to prevent evaporation, or they may be shaded with 

 paper or muslin. The soil should be moist before sowing, and 

 if further moisture is required before germination takes place 

 watering should be done with a very fine sprinkler, a better plan 

 is to place the pot or flat in a vessel of water, taking care that 

 the water is not deep enough to reach higher than one inch below 

 the surface of the soil. In all cases overhead watering of seeds 

 should be avoided if possible, as this operation is liable to puddle 

 the surface of the soil : if care is taken that the soil is thoroughly 

 moist before sowing it is rarely that watering is required until 

 after germination. 



Shading which has been placed over seeds should be removed 

 as soon as they germinate, and in rooms and greenhouics, pots 

 or flats of seedlings should have all the light possible and be 

 placed close to the glass, so as to prevent the young plants from 

 becoming drawn and spindly ; strong plants can never be produced 

 from seedlings of this character. 



It has been indicated that rapidity of germination is in alt 

 cases desirable, and this is naturally more easily accomplished 

 in a warm soil than in a cold one. While in the case of things 

 like melons, lima beans, and others native of hot climates, it ii? 

 useless to sow them until the soil is warm, the general rule for 

 hardier species like peas, spinach, and so on. is to sow them as 



