PROPAGATION BY SEED. 



311 



The larger seeds are, such as the acorn and 

 walnut, the deeper they should be placed; while 

 very small seeds, such as rhododendron, &c, 

 should be sown upon a smooth surface, and 

 scarcely covered at all. It is necessary, however, 

 that light be excluded until germination has 

 taken place. Moisture is necessary to germina- 

 tion, and without it seeds would ever remain 

 inactive. The quantity of moisture requisite to 

 cause germination in some seeds is much greater 

 than in others ; and hence pease, beans, &c, when 

 hasty vegetation is desired, are often soaked in 

 water for some hours before sowing; and in dry 

 states of the soil, the drills are watered before the 

 seed is committed to them. Decandolle found 

 that a French bean, weighing 544 milligrammes, 

 absorbed 756 of water. The grand secret of 

 keeping seeds in a good state in our seed ware- 

 houses is their being kept dry ; and if they 

 could be at the same time excluded from air, no 

 doubt their period of vitality would be consider- 

 ably lengthened. Absence of light is another 

 condition, as has been shown by M. Boitard and 

 others, almost indispensable to germination. In 

 the case of very small seeds which do not admit 

 of being covered with soil, germination will be 

 much assisted if they be covered with bell glasses, 

 either painted black or having a thick piece of 

 cloth laid over them. According to the recent 

 experiments by Mr Hunt, the luminous or light- 

 giving rays, and those nearest the yellow, have 

 a marked effect in impeding germination ; while 

 the red or heat-giving rays are favourable to the 

 process, if abundance of water be present ; while 

 the blue rays, or those concerned in chemical 

 action or actinism, accelerate the process and 

 cause rapid growth. 



The temperature necessary for the germina- 

 tion of seeds extends over a considerable range 

 in the scale of the thermometer. We have 

 stated that 32° Fahr. is the lowest with which 

 we are acquainted at which seeds will germinate, 

 because below that degree water freezes, and 

 cannot, therefore, be absorbed by the tissue of 

 the seed. It is possible, however, that some of 

 the less perfect plants, such as some of the Algse 

 and Fuci in the arctic regions, may vegetate even 

 below that point. The general range, however, 

 is from 45° to 80° or 90°. Some seeds, such as 

 the rose-acacia, Robinia, pseudo-acacia, and some 

 of the Australian acacias, have been immersed 

 for some minutes in boiling water without their 

 vitality being destroyed. In cultivation, some 

 require the heat of the tropics, while others 

 vegetate freely in the heat of our springs. The 

 highest limit of prolonged temperature which 

 cereal grains can bear in water is stated by Ed- 

 wards and Colin to be 95°, and the highest they 

 can bear in sand or earth, 113° Fahr. Dr Lind- 

 ley records a case of the seeds of the raspberry 

 having germinated after being subjected to the 

 boiling point of syrup, which is 230°. The seeds 

 of the annual poa, Poa annua, chickweed, Alsine 

 media, and various others, will germinate at very 

 little above 32°. These points may therefore be 

 taken as the maximum and minimum of vegeta- 

 tion. 



One seed producing twin plants. — In the ordi- 

 nary course of nature one seed produces one 



plant as a general rule ; but to this there are ex- 

 ceptions, one of which is stated by Mr Thwaites, 

 in " Annals of Natural History," as occurring in 

 the case of a single seed of a hybrid fuchsia pro- 

 ducing two plants " extremely different in ap- 

 pearance and character, one of them partaking 

 of the character of F. fidgens, and the other of 

 F. coccinea," these being the two parents. " It 

 cannot be doubted," he says, "that these very 

 dissimilar structures were the produce of one 

 seed, since they were closely coherent, below the 

 two pairs of cotyledon leaves, into a single 

 cylindrical stem, so that they had subsequently 

 the appearance of being branches of one trunk." 

 It is not improbable but the same thing fre- 

 quently occurs in the case of forest trees of 

 natural growth, where two apparently distinct 

 trees rise from one root — a circumstance ac- 

 counted for, but we believe erroneously, by sup- 

 posing two seeds to have sprung up together, 

 and that, from the closeness of their stems, a 

 species of natural engrafting had taken place 

 while they were very young. 



Vitality of seeds. — We have stated above, that 

 some seeds are supposed to retain their vitality 

 for two thousand years or more. There are 

 others, if placed under the ordinary conditions 

 natural to them, that lose that power almost 

 immediately after they have arrived at full ma- 

 turity ; many continue sound one year, others 

 two, and some few not only for a greater number 

 of years, but also being improved by keeping. 

 We are not aware that this latter fact has ever 

 been physiologically accounted for, but practi- 

 cally it is known to be the case. The following 

 common instances may be given. Melon and 

 cucumber seeds are improved by age, in so far 

 that they are found to be more productive of 

 fruit, and less prone to grow to branches than 

 when new ; cauliflower and most of the brassica 

 tribe are less liable to button or run prematurely 

 into flower ; while turnips bulb better, produce 

 less top, and are less liable to run to seed in 

 spring, when the seed is several years old, than 

 if the produce of the preceding season. If such 

 seeds, therefore, be well kept, we would say that 

 they were better when four years old than when 

 one year ; and, if this theory be correct — and 

 we think the experience of years goes far to 

 prove it so — that they are in a very fitting state 

 for sowing while under ten years. Gardeners 

 have long seen the importance of this, and hence 

 it is no unusual thing for many to carry about 

 seeds of the two first mentioned in their pocket, 

 that the necessary maturation may be accelerated 

 by the warmth of their bodies. We state this 

 latter case, not as an example to be followed, but 

 as an evidence of the principle. The object 

 aimed at in the cultivation of the plants we have 

 named is not bulk of gross vegetable matter, 

 but to insure an end ; and that end is to produce 

 those fruits and vegetables in the highest state 

 of perfection they are capable of arriving at, and 

 most fitted for the purpose for which they are 

 cultivated. 



A still more extraordinary instance than 

 those of the mummy wheat, &c, of the pro- 

 tracted vitality of seeds, is to be found in a paper 

 by Mr Kemp, published in the " Annals of Nat. 



