1919] Coit-Bodgson : Abnormal Shedding of Washington Navel Orange 291 



to 300 per cent. This is followed by dissolution of the gelatinous 

 walls, thus freeing the cells which are now surrounded merely by the 

 very thin and delicate tertiary membrane. No elongation of the 

 tertiarj' membrane has been observed. Neither has anj- cell division 

 prior to separation been seen to occur, although immediately following 

 separation this often takes place. So f|ir as ascertained, therefore, 

 ab.sei.ssion in the orange conforms to the usual type, e.g.. schizolysis'' 

 representing di.s.solution of the middle lamellae of the abscission zone 

 cells by hydrolysis with subsequent separation. 



Stimuli Leading to Abscission 



The direct cause of abscission in plants in general is considered to 

 be some stimulus which may be brcmght into play in a variety of ways, 

 depending somewhat on the nature of the plant involved. Lloyd'* has 

 taken pains to enumerate some of the different kinds of stimuli wliich 

 according to various writers have been found to cause abscission. It 

 is our purpose to consider these in turn as a possible cause of abscission 

 in the Navel orange anil possibly by elimination to arrive at the true 

 cause or causes involved. 



Mechanical Shock or Traumatic Stimuli 



Fitting" has shown that jarring or shaking the flower stalks of 

 Verbascum sp. and (rcraniiim pyrenaicum will result in abscission 

 within a few minutes. AVe were unable to produce like results with 

 Citrus by Ibis method. .Moreover, abscission has been observed to 

 occur regularly under conditions which would preclude the possibility 

 of this cause l)eing operative with oranges. 



An effort was made to eau.se abscission by cutting and bruising the 

 young fruits in various ways. The result was a failure in every case. 

 Exeis.sion of the style and petals either separately or together, either 

 before or during anthesis. failed to i)roduce abscission. Many of the 

 fruits from which the style had been removed developed to maturity 

 in a normal way. Otiiers abscissed but the reaction time varied so 

 widely as to make it very improbable that tiie removal of tlie style 

 was the stiimilus involved. 



I'Correns, Vermehruii^ der Laubnioosc, .Iciia, 1899. (CiteJ from Lloyd.) 

 n Abscission, Ottawa Naturalist, vol. 28 (1914), pp. 41-52, 61-7.5. 

 15 Untersuclninfjen iiber die vorzeitige Entbliitterun}; von Bliiten, .lahrb., f. 

 Wiss. Bot., vol. 4!) (1911), p. 187. 



