82 RE GENERA TION 



external factor, gravity, is also a factor in the regeneration of the 

 pieces, is abundantly shown by the experiments of Vochting and 

 others, but that innate factors are also at work cannot be doubted. 

 We find evidence in many animals of a similar difference between the 

 two ends of a piece, and we speak of this difference between the ante- 

 rior and posterior ends of a piece as its polarity. What this polarity 

 may be we do not know, and it is even doubtful whether we should be 

 justified in speaking of it as a force in the sense that the difference in 

 the ends of a magnet is the result of a magnetic force. The kind 

 of polarity shown by animals and plants does not seem to correspond 

 to any of the so-called forces with which the physicist has to deal, but 

 a further discussion of this question will be deferred to a later chapter. 



The preceding account of regeneration in some of the higher 

 plants has shown that their usual method of regeneration is by means 

 of latent buds that are present along the sides of the stem, or by 

 means of adventitious buds that develop anew along the sides of 

 the stem. In a few cases new buds may develop from the new tissue 

 of the callus that forms over the cut-ends, but in such cases the new 

 shoots, or the new roots, are much smaller in diameter than the end 

 from which they arise, and usually several or many new shoots de- 

 velop on the same callus. In these respects the regeneration of the 

 higher plants is different from that of the higher animals, for, in the 

 latter, the new part arises from the entire cut-surface. This differ- 

 ence is no doubt connected with differences in the normal method 

 of growth in plants and in animals, and an explanation of the growth 

 would, perhaps, also give an explanation of the mode of regeneration. 

 The normal method of growth in higher plants takes place largely by 

 the formation of lateral buds, as well as by terminal growth, and we 

 find that regeneration takes place in most cases from the same lateral 

 buds or from others of a similar kind that develop after the piece has 

 been separated. 



It is sometimes stated that the higher plants do not regenerate at 

 the cut-ends, because they produce buds at the sides. The statement 

 implies that there is some sort of antagonism between the regenera- 

 tion of a bud at the end, and the development of buds at the side. It 

 may be true that the development of a latent bud at the side might 

 suppress the tendency to produce a bud at the end, if such a tendency 

 exists ; but if we remove the lateral, pre-formed buds, new ones 

 develop at the sides, and not at the end. That there need not be an 

 antagonism between the formation of a bud, or of buds, at the end, 

 and also at the sides, is shown in Vochting's experiments with the 

 roots of the poplar. In these, leaf-shoots and root-shoots developed 

 both from the callus over the cut-end, and at the side of the piece also. 

 It has further been shown that, although a piece of the internode does 



