408 University of California Publications in Botany [VOL. 5 



8. Mature capsules of F H179 are apparently more sensitive to 

 injury than those of N. Langsdorffii (table 4, j). 



The table dealing with the experiments on Lycopersicum indicates 

 that flowers of this genus are remarkably resistant to injury, fall 

 occurring only as the result of stimulation when the ovary is injured 

 (table 5, c and d). Since a large number of tomato flowers are nor- 

 mally abscissed from the different inflorescences on a plant, the sev- 

 eral exceptions to the above statement noted in the table probably 

 demonstrate to what extent the normal physiological condition of the 

 plant affects the matter. It seems to be the opinion of most gardeners 

 who are familiar with the tomato plant that floral abscission in this 

 species is more dependent upon soil conditions than upon injury or 

 sudden changes in climatic conditions. It would seem, however, that 

 injuries to very young fruits normally cause fall, but in this case a 

 stage of development is soon reached at which injury to the berry has 

 no effect in inducing abscission (table 5, /). 



Taking the general results of all the experiments into consideration, 

 it is seen, in the first place, that where injury of a certain type causes 

 fall, a stage of development of the flower is soon reached beyond which 

 the injury no longer causes fall. The increase in resistance to the 

 stimulus of mechanical injury takes place gradually in the species 

 investigated, but some of the species are much more resistant than 

 others. In the second place, injuries to the ovary generally cause 

 flower-fall. Thirdly, whether or not flower-fall occurs as a result of 

 injury to other flower parts depends in some way upon the quantity 

 of material removed. Fourthly, injury to the pedicel does not cause 

 abscission unless it breaks entirely the cellular connection between 

 flower and stem. Lastly, it is improbable that fall induced by injury 

 is due to checking the transpiration stream, since injury to the ovary 

 could have no such effect. Also, a cut across the pedicel so that the 

 flower hangs by only a few tracheae must check transpiration from the 

 flower considerably, yet in this case no abscission occurs. 



It was suggested by Bequerel that injury might cause abscission 

 by checking the transpiration stream which passes up through the 

 pedicel. Considerable doubt has already been cast on this point in the 

 above discussion. In order to throw more light on this question the 

 following experiment was performed in an effort to determine whether 

 checking the transpiration stream . of itself and unaccompanied by 

 mechanical injury would cause abscission. 



Experiment 12. As a means of checking transpiration from the 

 flower a coating of paraffin seemed desirable because it hardens 



