1916] Goodspeed-Ayres: Sterility of Nicotiana Hybrids 287 



or fruit-fall. Especially in the case of nitrogen the results in many 

 cases contradicted the expectation in that flowers and young fruits 

 were retained almost as long on a plant growing in a rich nitrogen 

 culture as on one growing in a culture of low nitrogen concentration. 

 The same was true with regard to the other nutrients whose concen- 

 tration was varied or in some cases the plants under both low and 

 high concentration dropped their flowers at the same time. 



Balls (1912. p. 68) reports that "boll-shedding" in Egyptian 

 cotton results from the formation in the flower stalk of an absciss- 

 layer of "extreme simplicity." The stimulus inducing its formation 

 is, according to Balls, the result of deficient root-absorption or its 

 equivalent. Thus a disturbance in the water content of the plant is 

 followed by a "demolition of the delicate balance between root and 

 shoot" to produce shedding. There seems to be grave doubt as to 

 the correctness of Balls' interpretation of the histology of the absciss- 

 layer in cotton and we may quote Lloyd (1914. p. 65) with reference 

 to the significance of the water relation with regard to abscission : 



In general . . . we must conclude, in view of the effects of drought upon 

 trees and shrubs, that tliere is a relation between lack of water and defoliation, 

 but it is not possible to attribute abscission directly to a reduction of water 

 content such as may be measured. It may, however, result indirectly bv the 

 disturbance of some other relation. . . . very slight departures from the 

 normal condition of the environment in other regards are sufficient to cause 

 or to hasten abscission. 



Balls further states that non-fertilization is not an appreciable cause 

 of boll-shedding in Egyptian cotton, a situation evidently occasioned 

 l)y the lack of rain during the season when cotton is flowering and 

 not to be taken to mean that fruits develop readily without fertili- 

 zation. The initial stimulus for the formation of the absciss-layer 

 which causes flower and fruit-fall in tobacco is non-fertilization. We 

 have been able to show, however, that a lowering of the total amount 

 of available nutrients is effective in at least retarding the formation 

 of this absciss-layer while it has, on the other hand, been shown that 

 a variation in the concentration of an individual nutrient has little 

 or no effect in flie same direction. All the evidence at hand seems to 

 iiidicjile tliat maintenance or disturbance of general physiological 

 states or conditions of equilibrium is a more potent factor for initiat- 

 ing or iiiliihiling sliniuli or leactions than the action of specific 

 chemical substances. Conversely, also, many effects now assigned to 

 the action of such specific substances are more consistently explaiir'd 



