— 77 — 



observation that when young willow shoots are kept in a moist chamber, abscis- 

 sion may commence, but may be inhibited and is then followed by a condition of 

 oedema. The abscission cells then increase in size, become contorted, and tear 

 apart unevenly without however producing anything like abscission, (figure ii). 

 To see in turgor alone a means of tearing apart the abscission cells, w-hich in such 

 a form as Impatiens have very delicate walls, always along the plane of the mid- 

 dle lamella and with no single cells damaged to the extent even of a slight distor- 

 tion, is in my opinion to see too much. 



The course of abscission. Abscission does not begin at the same time and 

 proceed at the same rate everywhere in the layer but first occurs above the axil- 

 lary bud, and is last accomplished on the opposite side of the stems. In a stem 

 12 mm. in diameter, several days intervened between the beginning and end of 

 abscission. 



The position of the layer can be foreseen in stems sufficiently translucent by 

 a deepening of the green colour. In the thick stem just mentioned this deepening 

 of colour enabled me to plot out the position of the abscission zone six days before 

 any separation became evident. Less time is required by smaller stems. 



CITATIONS. 



1. Cook, Bassett et al. Piotective Enzymes. Science, n. s. 33, 624. Apr. 11 

 1911. 



2. Lloyd, F. E. Abscission in Flowers, Fruits and Leaves. Ottawa Natural- 

 ist, 1914 (In press.) 



3. Gortner, R. A. ahd Harris, J. A. An axial abscission of Impatiens 

 Sultani as the result of traumatic stimuli. Am. Jour. Bot. i : 48-50 1914. 



4. Correns, C. Vermehrung der Laubmoose, etc. Jena, 1899. 



5. \^on Hoehnel, F. R. Weitere Untersuchungen ueber den Abloesungsvor- 

 gang. etc. Mitth. forstl. Vers. Oest. 2: 247, 1879. 



6.\"oechting, H. Ueber Organbildung im Pflanzenreich. Bonn. 1878, 

 (through Ilannig.) 



7. Massart, J. La cicatrisation chez les vegetaux. !Mem. couronnes. ac. r. 

 de Belgique, 1898. (through Hannig). 



8. Loewi, E. Untersuchungen ueber Blattabloesung und verwandte 

 Erscheinungen. Proc. \'ienna Acad. Math.-nat. class. 1907. p. 983. 



9. — Hannig, E. L'ntersuchungen ueber das Abstossen von Blueten. etc. 

 Zeitschr. f. Bot. 6: 417, 1913. 



10. Tison, A. Recherches sur la chute des feuilles chez les Dicotyledones. 

 Mem. soc. Linn. Normandie. 20: 125, 1900. 



DESCRIPTION OF PLATE. 



All the figures relate to Impatiens sultani except figure 11 which is Salix sp. 



Fig. I. A. Abscission layer (ab) intersecting the plane of amputation 

 (c, c); 



B. Longitudinal and C. transverse diagram to show the portion 

 separated by abscission. 



Fig. 2. Superimposed abscission layers si and s2 in an internode amputated 

 at cc'. 



Fig. 3. Laternal axial abscission. A. Stem from which the leaf bases and 

 accompanying axillary buds are being separated by lateral abscission (al.^ in 



