■physiologically considered. 481 



come up at all that year, or singly and sickly; on which account, 

 even in the open air, there is a distinction between the autumn 

 and the spring seeds. This will be seen by the following ex- 

 periment. In May, 1838, I gathered, at Bonn, seeds of Z)raba 

 prse'cox. To be certain of the species, I sowed the seeds in a 

 pot by themselves, which I placed in an open pit (Kasten) with 

 other seeds which were to be kept cold, and ti-eated them the 

 same. Only two plants came up that year, of very stunted 

 growth, and never attained strength to flower ; while next spring 

 the remaining seed came up very thick and strong, and flowered 

 in the space of four weeks. Thus it may, in cultivation on 

 a large scale, be observed, that, of the seed which did not ger- 

 minate in spring, only a little comes up in summer; while late 

 in the season, when plants in the open air make a second 

 growth, more come up; and in the following spring, usually, the 

 remainder of the perfect seed comes up. Of the more difficultly 

 germinating seeds of several trees and shrubs, such as Mespilus 

 and others, it often happens that seeds of the same sowing come 

 up every spring after a lapse of three or four years. A great 

 portion of biennial plants make an exception to this rule : their 

 seed, being sown immediately after ripening, generally comes 

 up good and quickly, becoming strong plants before winter, 

 which usually flower the following year. Many, also, that are 

 cultivated as annual plants, show the same sort of developement; 

 but it is only those which live for a considerable length of time, 

 such as, for example, a great number of the Californian annuals, 

 which are now cultivated as ornamental plants. In their native 

 country they spring up before winter, and are preserved through- 

 out that season by a continual covering of snow. 



Moisture, heat, and oxygen are requisite for the process of 

 germination ; and if any of these three requisites is wanting, 

 germination is prevented. Darkness was formerly considered, 

 also, as one of the requisites for hastening germination : but it 

 is not founded on nature ; for, though we, in proportion to their 

 size, cover the seeds with sufficient earth to maintain an equal 

 moisture, we also scatter the smaller seeds, such as ferns and 

 heaths, on the surface, and produce the uniform moisture by 

 means of a glass covering. 



Moisture and oxygen, together with a small portion of 

 nitrogen (although it is doubtful whether the latter is necessary 

 to germination), are taken up by the seed, while the process of 

 assimilation (or digestion) is promoted by the heat. That the 

 want of moisture prevents the germination of seeds is well 

 known to every gardener ; and, on that account, we preserve 

 our seeds in the driest place we can command. The want 

 of oxygen and heat has, also, some effect, as the following will 

 show. If a number of seeds are put in a little water, which 



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