158 SCIENCE OF GARDENING. Pakt II. 



Sect. I. Germination of the Seed. 



716. Germination is that act or operation of the vegetative principle by which the em- 

 bryo is extricated from its envelopes, and converted into a plant. This is universally the 

 first part of the process of vegetation. For it may be regarded as an indubitable fact, that 

 all plants spring originally from seed. The conditions necessary to germination relate 

 either to the internal state of the seed itself, or to the circumstances in which it is placed, 

 with regard to surrounding substances. 



717. The first condition necessary to germinatio7i is, that the seed must have reached 

 maturity. Unripe seeds seldom germinate, because their parts are not yet prepared to 

 form the chemical combinations on which germination depends. There are some seeds, 

 however, whose germination is said to commence in the very seed-vessel, even before the 

 fruit is ripe, and while it is yet attached to the parent plant. Such are those of the tan- 

 gekolli of Adanson, and agave vivipara of East Florida, as well as of the cyamus nelumbo 

 of Sir J. E. Smith, or sacred bean of India ; to which may be added the seeds of the 

 common garden-radish, pea, lemon, &c. But these are examples of rare occurrence ; 

 though it is sometimes necessary to sow or plant the seed almost as soon as it is fully ripe, 

 as in the case of the coffee-bean ; which will not germinate unless it is sown within five 

 or six weeks after it has been gathered. But most seeds, if guarded from external injury, 

 will retain their germinating faculty for a period of many years. This has been proved 

 by the experiment of sowing seeds that have been long so kept ; as well as by the deep 

 ploughing up of fields that have been long left without cultivation. A field that was thus 

 ploughed up near Dunkeld, in Scotland, after a period of forty years' rest, yielded a con- 

 siderable blade of black oats without sowing. It could have been only by the plough's 

 bringing up to the surface seeds that had been formerly too deeply lodged for germination. 



718. The secojid condition is, that the seed sown must be defended from the action of the 

 rays of light. This has no doubt been long known to be a necessary condition of ger- 

 mination, if we regard the practice of the harrowing or raking in of the grains or seeds 

 sown by the farmer or gardener as being founded upon it. 



719. A third condition necessary to germination is the access of heat. No seed has ever 

 been known to germinate at or below the freezing point. Hence seeds do not germinate 

 in winter, even though lodged in their proper soil. But the vital principle is not neces- 

 sarily destroyed in consequence of this exposure ; for the seed will germinate still, on the 

 return of spring, when the ground has been again thawed, and the temperature raised to 

 the proper degree. But this degree varies considerably in different species of seeds, as is 

 obvious from observing the times of their germination, whether in the same or in different 

 climates. For if seeds which naturally sow themselves, germinate in different climates 

 at the same period, or in the same climate at different periods, the temperature necessary 

 to their germination must of consequence be different. Now these cases are constantly 

 occurring and presenting themselves to our notice ; and have also been made the subject 

 of particular observation. Adanson found that seeds which will germinate in the space 

 of twelve hours in an ordinary degree of heat, may be made to germinate in the space of 

 three hours by exposing them to a greater degree of heat ; and that seeds transported from 

 the climate of Paris to that of Senegal, have their periods of germination accelerated from 

 one to three days. - (Families des Plantes, vol. i. p. 84.) Upon the same principle, seeds 

 transported from a warmer to a colder climate, have their period of germination protracted 

 till the temperature of the latter is raised to that of the former. This is well exemplified 

 in the case of green-house and hot-house plants, from which it is also obvious that the tem- 

 perature must not be raised beyond a certain degree, otherwise the vital principle is totally 

 destroyed. 



720. A fourth co?idition necessary to germination is the access of moisture. Seeds will 

 not germinate if they are kept perfectly dry. Water, therefore, or some liquid equivalent 

 to it, is essential to germination. Hence rain is always acceptable to the farmer or gar- 

 dener, immediately after he has sown his seeds ; and if no rain falls, recourse must be 

 had, if possible, to artificial watering. But the quantity of water applied is not a matter 

 of indifference. There may be too little, or there may be too much. If there is too 

 little, the seed dies for want of moisture ; if there is too much, it then rots. The case is 

 not the same, however, with all seeds. Some can bear but little moisture, though others 

 will o-erminate even when partially immersed ; as was proved by an experiment of Du 

 Hamel's, at least in the case of peas, which he placed merely upon a piece of wet sponge, 

 so as to immerse them by nearly the one half, and which germinated as if placed in the 

 soil. But this was found to be the most they could bear ; for' when totally immersed in 

 the water they rotted. There are some seeds, however, that will germinate even when 

 wholly submersed. The seeds of aquatics must of necessity germinate under water ; and 

 peas have been also known to do so under certain conditions. 



721. A fifth condition necessary to germination is the access of atmospheric air. Seeds 

 will not germinate if placed in a vacuum. Ray introduced some grains of lettuce-seed 



