1918] Kendall: Ahscissio)! of Flowers and Fruits in 8ola,imce<ie 399 



esculent um, lochrorna tuherosa, Solanum nigrum, and *8^. verhasci- 

 foliuni, upon subjection to 3 per cent illuminating gas for twenty 

 liours, throw off all flowers up to those two or three days past anthesis. 

 No abscission occurred, however, in any concentration of gas, in 

 Nicotiana Bigelovii, N. quadrivalvis, y . multivalvis, Lycium australis, 

 Petunia hyhrida, Salpiglossis stinuata, or Salpichrora rhomhoidea. 



A peculiar condition exists in Solanum umhelliferum, Avhich throws 

 off buds in the illuminating gas but never under any conditions, in- 

 eluding temperature or the presence of narcotic vapors, throws off 

 flowers in which the corolla has fully opened. A corresponding con- 

 dition seems to exist in Nicotiana Tahacum var. macropliylla, FiHlSi, 

 iV. Sanderae, N. rustica var. hrasilia, and in one other variety of N. 

 rustica, all of which seldom under any conditions detach fully opened 

 flowers, although flowers up to that stage are freely abscissed. Thus 

 there seems to be, in certain species and at about the time of the open- 

 ing of the corolla, a sudden increase in resistance to the external 

 stimulus which is causing abscission. In other species this sudden 

 increase in resistance does not take place, abscission commonly occur- 

 ring at any stage in the development of the flower or fruit and the 

 increase in resistance taking place very gradually. In addition, there 

 seems to be an intergradation of forms between those in which the 

 increase in resistance takes place suddenly and those in which it takes 

 place gradually. 



The next subject to be taken up is a consideration of experiments 

 5, 6, 7. 8, and 9 on the induction of abscission in small isolated pieces 

 of the pedicel. The main purpose of devising these experiments was to 

 throw some light, if possible, on the direct or indirect action of the 

 external factor in causing "spontaneous" abscission. The pedicel of 

 F^ H17n was again chosen as material for the following experiments, 



Fij.'. !) 



