GERMINATION. 463 



are the so-called conditions of germination. The measure of each 

 which is necessary varies with the different kinds of seeds, according 

 to the chemical nature of the contents of the cells, of the cell-walls, and 

 their general structure. 



Water plants germinate best in water, land plants in damp earth. 

 Of the precedents of this process we know nothing at all. We do not 

 even know all the conditions under which starch is produced and de- 

 composed ; and those with which we are acquainted agree so little with 

 those presented in the germinating plant, that they can serve little 

 towards the explanation of the matter. The discovery of diastase by 

 Payen and Persoz made a great noise, and it was generally thought that 

 the key had been found ; but it was forgotten that diastase only dis- 

 solves starch at a temperature of from 65 70 C., and this temperature 

 is not found to exist in germinating plants, and, should it be produced, it 

 must destroy life. It is clear that only the decomposition of the carbo- 

 naceous substances is essential to the process of germination ; all remain- 

 ing phenomena belong solely to the processes of vegetation which appear 

 later. 



A more important point occurs here, namely, the direction which the 

 germinating plant takes. The examples of Viscum and Loranthus 

 prove that it is not a universal law of vegetation that the root should 

 grow downwards towards the centre of the earth, and that the .stem 

 should take a contrary direction. With the generality of plants this is 

 indeed the ordinary manner of growth. However the seed may chance 

 to fall, yet, in germination, the radicle so bends itself as to sink per- 

 pendicularly into the soil, whilst the stem rises perpendicularly from it. 

 The direction which the stem takes is, however, much modified by the 

 influence of light ; it is found to grow in the direction from which the 

 light comes : hence, if the light falls obliquely, the stem rises in a cor- 

 responding direction. Many theories have been invented to explain 

 this, and supported by the very interesting experiments of Knight *, 

 gravitation has been called into aid ; this only proves with what ob- 

 scure notions some persons are satisfied. Whether the experiments of 

 Knight would always give the same result is very doubtful ; but were it 

 so, they would yet be very insufficient to establish that gravitation is 

 the cause of this phenomenon, seeing that Viscum and Loranthus would 

 not fall within the law ; and the causes which determine the direction of 

 the growth of these plants are probably the same as in others. Gravi- 

 tation on the earth is in proportion to the mass and volume. These 

 are sometimes greater in the radicle, sometimes in the upper part of the 

 embryo ; hence, according to the usual law of gravitation, the plant 

 would sometimes grow in one way, sometimes in the other, which does 

 not happen. Moreover, as the radicle lengthens, it draws fluids from 

 the soil, and the contents of its cells are always more dilute and speci- 

 fically lighter than those in the upper parts of the plant ; hence it would 

 turn the root round, which being attracted least to the earth, would 

 ascend into the air. A cone falls to the earth upon its base ; we have 

 embryos of conical form, as well as of other forms, but both germinate 

 so that the radicle sinks into the earth, though it may be projected from 

 the point or base of the cone. No embryo germinates free, all remain 

 for a longer or shorter time enclosed in the testa or pericarp, from 

 which the embryo for some time only projects a small point : gravity 



* Trcviranus, BeStrage zur Pflanzcnphysiologie (in which the works of Knight 

 are translated). Gottingen, 181 1, p. 191. 



