306 Vniversity of California Tuhlicaiions in Agricultural Sciences [Vol. 3 



1. Referring again to plate 29, it is apparent that the excessive 

 number of buds oecasions a severe struggle for survival, only a com- 

 paratively small number being able to acquire water and food sufticieut 

 for development. As it is impossible to determine in advance which 

 if any of a group of similar buds Ls destined to remain, it is evident 

 that if the sterile .stigmas of all are inoculated just previous to open- 

 ing many will eventually fall from other causes, iloreover, the con- 

 siderable period of time involved and the frequent necessary opening 

 and closing of the bags in an atmosphere shown to be filled with spores 

 would introduce an element of serious error. Plate 40 shows one of a 

 number of trees u.sed futilely in efforts to get results in this way. 



2. Orange flowers are dimorphic, as before mentioned, a certain 

 number being destined to fall because the ovary is not capable of 

 development. The configuration of the navel is to a certain extent 

 fortuitous. In some cases the epidermal folds are so adju.sted a.s to 

 admit infection, in others not. It is obviously out of the question to 

 examine each frviit frequently and with sufficient minuteness to deter- 

 mine whether dui-ing growth an opening sufficient for the entrance 

 of the fungus was or was not available. 



3. A species of aphis is very common on Malva and other weeds 

 under the trees. For some reason not at present clear, the insect is 

 unable to increase to any extent when feeding on the orange leaves 

 in the open. However, it was found that whenever a twig was enclosed 

 in H paper bag or a tree enclosed in a cheesecloth tent (pi. 40) the 

 aphis multiplied at an astonishing rate. In about half the bags on 

 the tree .shown the twigs were defoliated and killed by the sudden 

 development of a mass of aphis from young and minute individuals 

 which were inadvertently included within the bags in spite of all pre- 

 cautions. 



.Summing up the relation between Alternaria and that part of the 

 June drop with which it is always associated, we have to conclude that 

 inasmuch as the presence of the fungus and its ability to provide a 

 certain stimulus have been demonstrated, it is not unreasonable to 

 suppose that abscission may be another manifestation of the same 

 stimulus both in the case of Navel oranges and in the apple varieties 

 referred to above. Satisfactory scientific evidence of this point, how- 

 ever, is lacking as yet. 



