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GARDENERS' CHRONICLE 



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E i 



I A Lesson on Plant Physiology and the Plant in | 



I Relation to Its Environment | 



§ Eeing One of a Series of Lessons of a Home Study Course on Gardening, Appearing Regularly in The Gardeners' Chronicle 1 



I Under the Direction of ARTHUR SMITH | 



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IMMEDIATELY after the union, or fusion, of the single 

 staniinate and pistillate cells, respectively, otherwise known as 

 fertilization, has taken place, the embryo commences to form. 

 In cross-fertilization this enil)ryo contains all the characters of 

 two lines of ancestors, which characters will continue to remain 

 part of the germ-plasm tif the resulting plant, and which are not 

 radically changed or added to by differences in environment. 

 At the same time some characters may become more dominant, 

 and others more or less repressed, but not extinguished, by 

 differences in food, soil and climate. 



One of the most important parts in the art of gardening is 

 the working out of methods of supplying such food, soil condi- 

 tions, etc., and in greenhouses, temperature, which, all together, 

 are known as environment, which will best conduce to the domi- 

 nance of the characters most desired. 



As soon as the embryo comes into existence, the deposit of 

 food for its sustenance during the period of germination com- 

 mences, resulting in the formation of the body known as a seed. 

 While sometimes an enlarged fleshy ovary, popularly known as a 

 fruit, is brought into existence without the formation of seed, as 

 in the case of the banana, yet, so far as I am aware — except 

 sometimes indirectly in what are called alternations or genera- 

 tions — seed is not produced unless the ovule is fertilized and an 

 embryo formed. In this connection, Nature obviously does not 

 consider it necessary to store up food for an embryo which does 

 not exist. This can easily be observed wlien shelling peas. Some 

 pods will be found to be perfectly full, others will contain some 

 full-sized peas and also some tiny peas which have evidently 

 stopped at the initial stage of their growth : these latter are 

 unfertilized ovules. 



.Seeds contain all the necessary ingredients for the building up 

 of the plantlet which results when the embryo starts to grow, or 

 commences to germinate, which germination is not complete 

 until the plantlet is able to gather its own food from the soil 

 and air. Plant food is stored up in the seed in the form of proteids, 

 carbohydrate (starch), fat and mineral salts. The proportions 

 of these ingredients vary in seeds of different genera and species. 

 Thus in corn, wheat, and in other seeds from the same order of 

 plants, starch is the predominating ingredient; in le;umincus 

 plants, such as peas and beans, proteid occupies the larger posi- 

 tion : while the seeds of flax and cotton are remarkable ft r their 

 excess of fat. which fat is extracted in the well known cotton- 

 seed and linseed oils. These stored up materials have to undergo 

 certain changes before they can be utilized by the germinating 

 embryo, the manner of this will be taken up later. 



As seeds of their kind vary in size, there is a greater amount 

 of total plant food in heavy than in light weight seeds, and the 

 additional reserve food in the larger seeds enables the plantlet 

 not only to reach a more advanced stage cf growth before 

 being compelled to collect and assimilate food from outside but 

 the two processes may go on together. Also the largest seeds 

 invariably contain the strongest embryos, therefore the combina- 

 tion of an especially virile embryo and an extra supply of food 

 will, all other things being equal, result in a plant of considerably 

 greater vigor than would be the case from small seeds. 



This has been practically proved, amongst other ways, by 

 commercial growers of lettuce under glass, who are able by 

 only sowing large seeds to raise one more crop during the Winter 

 than when unsifted seed is used. In all cases it is therefore 

 cheaper to pay more for properly screened seeds. 



ft would seem scarcely necessary to emphasize the importance 

 of quality and potential vigor of seeds in crop production, or in 

 other words, their capability to produce the most vigorous plants 

 of which the variety is capable. .Another important consideration 

 is the inherent adaptability of the strain of seed to the environ- 

 ment under which it is to be grown. 



These considerations as a whole will be affected by the environ- 

 ment of its parents, in which connection the most important points 

 are cultural conditions, soil and climate, and there is no doubt 

 whatever that some strains of seed are better adapted, and will 

 therefore produce better results, under some environments than 

 they will inidor others. Hitherto- this point has received little or 

 no consideratii n from sardeners, although some large commercial 

 growers are aware that seeds produced on certain soi's give bet- 



ter returns than those grown upon soils of an opposite character, 

 and they act accordingly. Some further points connected with 

 this were considered last month. 



In harvesting seed crops, careless methods may produce seed 

 not only of a poor germinating percentage due to the embryos 

 being killed, but may also cause the embryos to be wanting in 

 vigor, so that even when germination takes place they may not 

 have strength enough to produce a plant, and in any case a plant 

 from a weak embryo is never at any period of its life so vigorous 

 as a plant from a strong one. The duration of an embryo's 

 vitality after the seed has ripened varies with the seed's maturity 

 when harvested and w-ith the conditions under which seed has 

 been stored, hut why this vitality is more enduring in some 

 species and less so in others, we cannot tell. The fact remains 

 that while seeds of some species will retain the power of germi- 

 nating for many years, others will lose this power in a few days 

 or weeks. The difi^erence in the time which seeds of various 

 species remain viable are, in one respect, irrespective of the 

 conditions under which seeds are kept ; that is to say, it matters 

 not how perfect these conditions may be. the embryos in certain 

 species of seeds will only remain alive for a certain limited 

 period. At the same time, with .-.pecial precautions and treatment, 

 there is no question that the life of seeds may be greatly pro- 

 longed beyond that which we know at present, though never for 

 centuries as is sometimes stated. Cases so reported cannot be 

 taken as evidence of the longevity of seeds. 



Numerous assertions have been periodically made about the 

 longevity of seeds which are of little value froin lack of detail 

 and of sufificient proof. The most notorious are those concerning 

 seeds from the sarcophagi of Egy^ptian mummies. It is now 

 generally acknowledged that no adequate proof of this germina- 

 tion has been produced, the reputed success in connection with 

 mummy wheat for instance, being due to the duplicity of .-Krab 

 relic vendors — in which characteristic they are not at all singu- 

 lar — in palming off modern seeds as being taken from sarcophagi. 



The average life of seeds varies greatly with different families, 

 genera and species, but there is no relation between the longevity 

 of plants and the \iable period of the seeds they bear. The seeds 

 of trees as a rule lose their vitality sooner than those of annual 

 weeds, for instance. Seeds of coniferous trees lose their vitality 

 in a year or so. and in the case of the Elm, unless its seed germi- 

 nates within a few days after it falls its power of doing so is 

 lost. It is a matter of common knowledge that many seeds 

 of plants classed as weeds may be buried in the soil for some 

 years and then germinate when brought near the surface. In 

 this latter connection the old saying that "one year's seeding 

 makes seven years' weeding" is easily understood, which would 

 be equally true if the word "ten" were substituted for seven. 



The question here arises regarding the advisability of keeping 

 unused seeds over from year to year. It has long been known, 

 and we have previously stated it, that the conditions under which 

 seed plants have been harvested and the degree of maturity at 

 the tim.e cf harvesting are factors which play an important part 

 not only in the percentage of germination immediately after 

 harvest, but also in the duration of the seeds' vitality. 



Apart from the fact that some seeds have to be sown as soon 

 as ripe and are therefore not handled by seedsmen, there are 

 many kinds which, while their vitality may lie retained for some 

 years if stored under proper conditions, soon become useless 

 when such conditions are detrimental. Many investigators have 

 learned that the rapidity with which seeds with more or less long- 

 lived potentialities lose their power of germination varies greatly 

 with the section of the countrv in which thev are kept. The 

 loss of vitality is especially marked in the case of seeds stored 

 in places of relatively high htniiiditv. The rapid deterioration of 

 seeds in localities having a humid atmosnhere has become a source 

 of much embarrassment to seedsmen. Many difficulties in shipping 

 seeds to the Gulf of Mexico for instance are a matter of com- 

 inon experience, as in that district seeds, which in other localities 

 keep for some years, lose their vitality in a few months. Expcri- 

 ineuts witli twelve species of garden seeds, stored midcr identical 

 conditions otherwise, possesed the power of .germination after a 

 lapse of six months, 60 per cent greater at -\nn .^rbor, Mich., 

 tlian at Mobile. .Ma. This shows that seeds retain their vitality 



