Section V, 1920 [17] Trans. R.S.C. 



Abscission of Fruits in Juglans Californica Quercina^ 

 By Francis E. Lloyd, F. R.S.C. 



(Read May Meeting, 1920) 



During the study of abscission of fruits in the cotton (Gossypium 

 herbaceum), a brief account of which was presented to this Society in 

 1915,2 it was found that those fruits which were shed were always 

 undersized to an amount approximately corresponding to the period 

 required for abscission. It is apparent that the slowing up of growth 

 is to be referred to a cause which indirectly results in abscission. This 

 cause is to be found in limited water supply. One factor involved in 

 bringing about this limitation is the capacity of the stem tissues to 

 transmit enough water to keep up the constant distension necessary, 

 and this becomes the more difficult as the number of fruits and other 

 water-absorbing parts on a particular stem increases. MacDougaF 

 found the water deficit of the stem supporting the fruits to be 25 per 

 cent of its volume in the species under consideration. It is evident 

 that when several fruits are borne in a raceme, as is the case in this 

 species, the possible discrepancy as between the transmission capacity 

 of the stem and the demands of the fruits must frequently lead to 

 poor development and loss. That this condition obtains in Juglans 

 californica quercina seems clear, for, though several fruits pass through 

 the earlier periods of development, sooner or later usually all but one 

 are lost by abscission. Practical proof of this was obtained during the 

 course of taking auxographic records of fruits during the summer of 

 1918 at Carmel, Calif. Dr. MacDougal was kind enough to place at 

 my disposal two records of growth in fruits which finally dropped ofï. 

 These records (for the periods June 19-30 and July 2-5, 1918) are 

 unique, the former more especially, in presenting graphically the 

 growth behaviour previous to and during the abscission period. They 

 were obtained by means of a compound lever, amplifying 10 to 40 

 times, according to setting, the taking arm resting on the fruit as it 

 lay properly supported on its side on a firm base. The dimensional 

 changes recorded were, therefore, linear and transverse to the axis of 

 the fruit. The fruits, the growth of which was thus measured, were 

 about 15 mm. in diameter. The writing arm made the record on a 

 revolving drum. 



^ Babcock. Digest, Annual Rep. Carn. Inst., Wash., 1918, p. 76. 

 2 Trans. Roy. Soc. Can. sen 3. 10: 55-61, S. 1916. 



' D. T. MacDougal. The Daily Course of Growth in Two Types of Fruits. 

 Carn. Inst. Wash. Ann. Rep. 1919, p. 69. 



