1918] Kendall: Abscission of Flowers and Fruits in Solan-aceae 351 



discussed by Lloyd (1914a) for Ampelopsis and Gossypium. In the 

 latter, abscission, in the abnormal case, occurred down the internode 

 at the base of the pedicel. This is explained as the result of a dis- 

 placement during growth by which part of the pedicel becomes united 

 to the stem. 



Occasionally, grooves or swellings are noticed at the base of the 

 organ being abscissed where they correspond more or less exactly to 

 the general position of the separation layer. Examples are given by 

 Hannig (1913) for Lycopersicum and Solatium tuberosum and by 

 Balls (1911) for Gossypium. Abscission may occasionally occur, 

 according to Lloyd (1914a), above a small bract. According to these 

 latter investigators, there is more often no external indication of the 

 layer. Frequently, grooves bear no relation to the layer because in 

 many cases of this kind (Hannig, 1913, for Brunfelsia) separation 

 occurs a short distance distal to the groove. 



From the above brief summary it is evident that in the case of 

 axial abscission the separation layer is located at or near the base of 

 an internode. Apparent exceptions are reported by Hannig (1913) 

 in which it is seemingly located at the middle of an internode. It 

 seems probable that a more critical re-examination might reveal the 

 fact that even these exceptions accord with the general rule. In these 

 cases, for example, the pedicel of the flowers in question might be 

 composed of two internodes. 



6. ORIGIN OF THE SEPARATION LAYER 



Kubart (1906) states that the occurrence of the separation layer 

 in all tyes of abscission may be explained in one of the three following- 

 ways: (a) the separation layer is preformed and represents simply 

 a portion of the primary meristem which has remained in its original 

 active state; (6) it represents a secondary meristem; (c) the primary 

 meristem may function directly as a separation layer. The differ- 

 ence between a and c is only a difference in time, c being added to 

 explain the origin of the separation layer in abscission of very young, 

 embryonic tissues. In a, the separation layer is present at the base 

 of the organ from the start of its development, but in b this layer has 

 to be formed by a secondary meristem before abscission can occur. In 

 a, cell divisions are not normally found preceding abscission, but in b 

 and c they are. Mohl (1860), working on the fall of the flower in 

 Aesculus, Pavia, Lagenaria, Cucumis, and Ricinus, states that the 

 separation layer in these forms is of type b. Throughout his entire 



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