66 



CASSELL'S POPULAR GAEDEXING. 



this kind are only made when the j)lants are new and 

 their nature unknown. The majority of cultivated 

 plants, for the reproduction of which seeds are relied 

 upon, are well enough understood to prevent errors of 

 treatment. It may be laid down as a general rule 

 to be observed in the treatment of all seeds, that the 

 temperature most suited to their germination and 

 vigorous development should never be below the 

 mean ground temperature in which the plant grows 

 naturally, but if possible should exceed it by several 

 degrees. Many seeds will germinate, though very 

 slowly, in a lower temperature than is good for them. 

 A high temperature will, on the contrary, force all 

 seeds into quick activity. Thus Peas, Beans, and 

 numerous other seeds of quick-growing herbaceous 

 plants which grow out of doors with us, will in a 

 temperature of SO'* germinate in about one-sixth the 

 time they take when sown in a more natural tempe- 

 rature. With proper care, a degree of heat much in 

 excess of what would prove sufficient may be applied 

 to seeds and plants, ofte-n to their advantage. The 

 limits of high temperature for plants are not so 

 strictly defined as the lower limits of temperature 

 are. It is possible thf^t plants do not object so much 

 to extreme heat as to extreme cold, a possibility ex- 

 plained by physiological laws. For horticultural 

 purposes a high temperature often proves of service in 

 the raising of plants from seeds. By sowing seeds 

 of hardy plants and trees in a stove temperature, 

 much time is saved, without any injury to the 

 seedlings resulting. A high temperature will induce 

 old seeds to germinate, which in a lower or more 

 natural temperature would not be excited into growth. 

 " Trial " seeds of vegetables. Wheat, &c., when sown 

 in a warm house to test their health have germinated 

 satisfactorily, but seeds of the same sample when 

 sown out of doors remained inactive. Their vital 

 force had become weakened by some cause or other, 

 and it was only under the exciting influences of a 

 high temperature that this could be remedied, and 

 the seeds made to germinate. 



The application of unusual warmth sometimes 

 fails to excite into germination seeds which require to 

 lie dormant for some time, or which do not mature 

 until some months after they have ripened. Thus 

 Acorns, Chestnuts, and other seeds of hardy trees 

 were sovm last autumn in a warm house, but refused 

 to germinate, although they remained healthy and 

 apparently uninfluenced by the warmth. Lilium 

 seeds, which out of doors often take from one to 

 two years after sowing before they germinate, 

 will, when sown in a warm house, be forced into 

 growth in about three months. On the other hand, 

 some kinds of seed ^dll germinate much more 

 quickly if sown just before they are ripe than if 

 allowed to mature before being sown. 



In all cases, however, a moderately high tempe- 

 rature will be found a useful factor in the raising of 

 plants from seeds, and especially when applied to 

 old seeds or those of questionable health. For seeds 

 of tropical plants a temperature of 80'* will be found 

 suitable in every case ; seeds from temperate climes 

 will germinate freely in a temperature. of 65" ; those 

 of hardy plants may be sown out of doors or in 

 frames in the season at which they would naturally 

 germinate. Where it is found convenient to employ 

 a higher temperature for seeds than they naturally 

 require, some care is necessary after germination 

 has taken place, as, although the excessive heat is 

 productive of good in so far as quick germination is 

 desired, it would have an injurious effect on the 

 health of the seedlings if they were allowed to 

 remain in a high temperature too long. As soon, 

 therefore, as they are strong enough, they should be 

 gradually hardened off till brought into the tempe- 

 rature most suited to them. 



Eeference may here be made to the effects of climate 

 on the characters of cultivated j)lants, and es^Decially 

 of those varieties which are the result of cultivation. 

 Xumerous facts are on record, tending to show 

 that such plants often owe their most important 

 characters to changes in the conditions of life, and 

 amongst these climate is a great modifier. Varieties 

 of Asters, Stocks, and Eoses, as well as of numerous 

 vegetables, which have originated with Continental 

 growers, often lose the character for which they 

 were distinguished after having existed for a time 

 in English gardens. For hardy plants, therefore, it 

 wiU be advisable to obtain seeds only from those 

 countries whose climate corresponds with our own. 



Moisture. — We sow seeds in soil, not because 

 the chemical nature of the soil itself has any in- 

 fluence on the germinating process, but because of 

 its being a suitable medium in which the conditions 

 essential to germination — i.e., warmth, moisture, and 

 air — are brought to bear upon the seed ; it also is 

 there ready to receive the roots of the seedling as 

 they develop, and to supply the plant with food as 

 soon as it begins to shift for itself. Moisture and 

 heat are two principal causes of germination ; with- 

 out them germination is impossible. The water 

 supplies oxygen sufficient to enable the seed to 

 get rid of the large amount of carbon which was 

 necessary so long as the seed remained dormant, but 

 which alone was detrimental to gTOwth. Water also 

 has a softening influence on the often hard shell in 

 which the seed is enclosed, thus rendering the 

 escape of the embryo from the seed much easier 

 than if the outer coats remained hard. To afford 

 the seeds the amount of moisture they require, we 

 either bury them in moist soil or sand, or place 



