1918] Kendall: Absciss^ion of Flowers and Fruits in Solariaceae 355 



rapidity and regailarity of reaction, Fitting claims that abscission is 

 a semi-tropistic phenomenon and suggests the term "Chorismiis" to 

 designate this type of reaction. 



It has been observed by Hannig and Fitting that the presence of 

 various narcotic vapors in the atmosphere around certain species of 

 plants causes their flowers or merely the petals to be thrown off. 

 Various aspects of this general problem of the reaction of plant tissues 

 to such agencies have been investigated. It has been determined by 

 various plant physiologists that the presence of narcotic vapors, such 

 as illuminating or acetylene gas, in the air around certain plant tissues 

 causes the proportion of soluble carbohydrates within their cells to 

 increase. This increase in the amount of soluble carbohydrates would 

 indicate an increase in cell turgor. The question at once arises, 

 whether or not this increase in turgor can effect complete separation 

 or maceration of cells without the occurrence of chemical alteration in 

 the walls. Richter (1908) resting his ease on experimental evidence, 

 throws some light on this problem. Various kinds of plant tissues 

 which he subjected to acetylene vapors broke in pieces because of the 

 maceration and collapse of the living cells within. He finds that in 

 the case of the cells of tissues which are commonly rich in starch 

 inclusions, such as the fruit of the snowberry and the potato tuber, 

 the maceration is most complete. In the potato, for example, 3 to 

 5 mm. of material on the surface become completely macerated after 

 being subjected to acetylene gas. According to Richter and Grafe 

 (1911), the proportion of sugar in starchy seedlings subjected to 

 acetjdene gas is larger than in seedlings grown under normal condi- 

 tions. In seedlings from oily seeds, however, the amount of sugar is 

 decreased and the proportion of glycerine and fatty acids increased. 

 The conclusion is therefore drawn that the subjection of plant tissues 

 to narcotic vapors favors the hydrolysing process in the cells involved. 

 The work of these two investigators goes to show that narcotic vapors 

 ma}^ cause abscission by acting in either of the most important meth- 

 ods suggested as responsible for cell separation ; they may increase cell 

 turgor on the one hand or favor the hydrolysis of the middle lamella 

 on the other. 



Lloyd (1916a) presents evidence of chemical change in the cell 

 walls of the separation laj'er before abscission. These cell walls stain 

 in the usual manner with iodine, giving a light brownish color, but 

 as abscission commences, they give a faint blue color when stained 

 with iodine and washed out with water. Shortly before cell separa- 



