644 PHYSIOLOGY. 



Germination. 



Requisite conditions. Given a properly ripened seed with 

 well-formed embryo, the period when the latter will begin to 

 sprout or germinate varies according to the particular species, 

 and according to external conditions. The general conditions 

 favouring germination are exposure to a certain temperature, a 

 certain amount of water, and access to oxygen gas, besides 

 certain secondary or accidental influences. As regards tem- 

 perature, germination may be carried on in some cases even at 

 freezing-point; but it is rarely manifested beyond 40-42 C., 

 though vitality is not necessarily destroyed at much higher tempe- 

 ratures. The actual temperature most conducive to germination 

 varies in different species. 



Sachs's experiments on the growth of Wheat and Barley show 

 that germination began below 5 0., in the French Bean and 

 Maize at 9 C., and in the Gourd at 13 C. ; but when the reserve 

 material in the seed was used up, and the seedling had to procure 

 its food from without, a higher temperature w 7 as needed. The 

 highest temperatures noticed by Sachs are, for Trench Beans, 

 Maize, and Gourds 42 C. ; for Wheat, Barley, and Peas 37 or 

 38 C. 



Water is a primary requisite in the germination of seeds, as it 

 softens the tissues and enables the insoluble reserve materials to 

 assume a soluble form. Free access to atmospheric air, or to the 

 oxygen contained in it, is necessary for the carrying on of those 

 chemical changes which are manifested during germination. If 

 seeds be deeply buried, so that access of air be prevented, they do 

 not germinate. 



Weak solutions of chlorine, iodine, and bromine have been 

 known to accelerate the process of germination, and camphor is 

 also stated to be a stimulant to the growth of the embryo plant. 



Effect of Electricity. Electric currents are stated to hasten 

 germination. When seeds are exposed to the action of galvanism, 

 it is found that those around the negative pole of the battery ger- 

 minate much more freely and quickly than those around the posi- 

 tive pole, and than those not submitted to the electric current. 

 Bridgeman, in 'Gardeners' Chronicle,' Feb. 1, 1873, further notes 

 that the radicles of the blackened and shrivelled seeds round the 

 positive w 7 ire grew upwards into the air instead of downwards ; and 

 this observation confirms a similar one made by Blondeau. 



Time required. Many seeds germinate very quickly when placed under 

 favourable conditions, especially those of Cruciferae, Grasses, manyLegu- 

 minosse, Cucurbitaceae, &c. ; but the period varies even in seeds of the 



