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This various behaviour appears to be connected writh the condition of the axillary- 

 buds as suggested by Gortner and Harris. In spite of the presence of small 

 leaves (a few mm. long), unless the buds are able to develope promptly or if they 

 are wilted badly and unable to recover, several internodes are shed in one piece 

 whether injury has been made use of or not. Whether therefore what remains 

 of an injured internode only falls, or one or more additional internodes are shed 

 at once, depends, as Hannig showed in the case of the leaf, on the presence or 

 absence of a minimum amount of leaf surface, since small entire leaves may not 

 be sufficient to prevent abscission. 



Gortner and Harris found it difficult to decide how near to the future abscis- 

 sion layer the cut which induces it could be made, and still be followed by it, since 

 the cut surface dried up, and since it was difficult to tell whether a thin layer of 

 cells has been separated off by abscission or not. I find that, if the surrounding 

 air be kept moist enough to prevent drying out, abscission intersects may occur 

 within a mm. of the cut, or, if the plane of future abscission intersects that of the 

 injury, the abscission will proceed to intersect it actually. It would seem that the 

 position of the cut has little, if any, influence on the position of the abscission 

 layer, so that normally, if the cut is made below it in position, abscission of the 

 low stump that is left will not occur. Inasmuch as the abscission layer is fre- 

 quently very oblique, it would be difficult to make a cut quite near to the base of 

 the internode which would certainly prevent abscission in all cases, or even in 

 many. 



However, the case of superimposed abscission layers, presently to be de- 

 scribed, together with some other cases of injury by amputation in different posi- 

 tions, suggests caution in deriving any strict conclusion, for in these instances 

 the abscission layer may have occurred higher up than normally, and indeed seems 

 to me to have done so. One case is worth mentioning. The cut was made about i 

 mm. above an axillary bud and somewhat obliquely, and the abscission layer which 

 was subsequently formed intersected the plane of amputation as indicated in figure 

 la-c. T found however that instead of passing through the pith at the expected 

 position, the abscission layer skirted around the stele. In this instance the opera- 

 tion appears to have modified the position of the abscission layer. 



It may happen (I have observed it in one instance) that two superimposed 

 abscission layers may be formed, the upper first, the lower appearing 2-3 mm. be- 

 low it (figure 2). This recalls the case of the leaf of Hauiamclis observed by 

 Tison (10), in which however the behaviour is normal, the second abscission en- 

 suing in the early spring. So far as I am aware this behaviour has not been ob- 

 served in other plants, but will doubtless occur oooasionally. 



Still more unexpected, but more frequently to be seen, is the abscission of 

 the leaf base and its accompanying axillary bud, and which I shall call lateral 

 axial abscission. It is quite distinct from true leaf abscission, since it occurs after 

 the leaf has been shed, and lies wholly within the stem tissues with the exception 

 noted below. The abscission layer is approximately hemispherical, the curve pass- 

 ing through the vascular tissues of the stem and penetrating as far as the center 

 of the pith (figure 3-b). It enters the stem a short distance above the axillary bud, 

 and comes out in a similar position below the leaf base, but may occasionally pass 

 through it (figure 3d), as shown in the figure. With respect to the leaf base the 

 abscission layer is then almost longitudinal. This kind of abscission may occur also 

 in conjunction with transverse abscission, the two being confluent (figures 3a-b) ; 



