the Vitality of Seeds by an Electrical Method: 



81 



The three cases are indicated 4 as above, and it should be stated that 

 in addition to the test of direction, electromotive force (which on my 

 plan of investigation can always be approximately ascertained) serves 

 to make the diagnosis easy in the great majority of instances. The 

 electromotive value in the case of an ordinary blaze current greatly 

 exceeds that of an ordinary polarisation-current {e.g., the former on 

 vigorous seeds may reach 0*1 volt, while on the same seeds the 

 polarisation-current similarly observed, was between 0*0005 and 

 0*001 volt). It is only in the case of weak or moribund seeds that 

 there is any room for uncertainty in the answer, by reason of a weak 

 blaze current in conflict with the weak polarisation-current. But the 

 vitality of such seeds, although we may be unable to assert that it has 

 fallen to the zero level, is insufficient for germination, and as tested in 

 the incubator at 25° such seeds have to be registered as dead. 



The principal points of the preceding statements may be illustrated 

 by the following experiment, which I give as being typical ; the 

 expressions " positive " and " negative " signify that the currents 

 respectively pass upwards from B to A, or downwards from A to B, 

 through the seed. 



Typical Experiment. — A freshly shelled out and unbruised bean set 

 up laterally* between unpolarisable electrodes gives — 



1. Blaze current in the positive direction in response to an induc- 



* I have given this typical experiment only to represent main facts without 

 details concerning differences according to strength of excitation, interval between 

 successive excitations, temporary abolition by excessive excitation, recovery of 

 capecity for reponse after injury, &c, &c. These and other points will be dealt 

 with in a more detailed and comprehensive account of the phenomena. It should, 

 however, be remarked at this stage that the lateral position of a bean, so that an 

 exciting current traverses both cotyledons normally, is chosen as being the least 

 asymmetrical and by reason of the situation of the embryo less liable to involve 

 physiological inequality than a longitudinal disposition. The comparison of effects 

 on the embryo proper and on the detached cotyledons shows that although all parts 

 of the seed give the blaze effect, the latter is greater in the embryo than in the 

 cotyledons at the outset of germination, and that in an abortive germination it 

 disappears from the embryo sooner than from the cotyledons ; e.g. — 



Cot. i. 



Radicle. 



Cot. 2. 



*0050 



-0625 



-0020 



nil 



-0180 



-0015 



-0060 



-0170 



*0040 



The plumule gave generally a smaller effect than the corresponding radicle. 

 The peeled-off testa gave no blaze whatever, and was evidently dead; its 

 polarisation counter-currents were relatively considerable. For these and other 

 reasons I prefer to test the isolated radicle rather than the entire seed. 



