PLANT PHYSIOLOGY 219 



of illumination falls within certain limits. Under ordinary 

 climatic conditions flowering and fruiting therefore occur at a 

 definite period of the year, but if the daily illumination is 

 artificially reduced, the time for flowering and fruiting to take 

 place is also reduced, while if the daily period of illumination 

 is lengthened, the flowering and fruiting stage is reached 

 correspondingly later. The authors thus regard it as possible 

 by artificial means to produce flowers and fruit at any season 

 of the year. The results wdth tobacco may be cited as examples. 

 With daily fight periods of 12 hours the plant required 152 to 

 162 days to flower, with illumination for 7 hours only in every 

 day the period was reduced to 55 to 61 days. How far these 

 results can be applied to all species of plants remains to be 

 seen. 



Wind is a side factor of some importance in regard to fruit 

 production. It may act directly by damaging the flowers and 

 by causing the evaporation of the stigmatic fluid excretion so 

 that pollen does not adhere to the stigma, or it may act indirectly 

 by interfering with the work of polfinating insects. M. J. 

 Dorsey {Journ. Agric. Res., 17, 103-126, 191 9) states that the 

 unfavourable action of wind is generally more pronounced in 

 the early stages of the flower than in the later. 



In horticultural practice it is an important question whether 

 spraying with arsenical, copper, and other sprays has any 

 effect on fruit production. While W. L. Howard and W. T. 

 Home {California Agric. Exper. Sta. Bull., 326, 1921) report 

 that no interference with the production of fruit takes place 

 when apricots in flower are sprayed with lime-sulphur mixture 

 or weak Bordeaux mixture, C. W. Edgerton (" Delayed 

 Ripening of Tomatoes caused by Spraying with Bordeaux 

 Mixture," Louisiana Agric. Exper. Sta. Bull., 164, 16 pp., 

 191 8) found that spraying tomatoes with Bordeaux mixture 

 brought about a delay of about one or two weeks in the ripening 

 of plants which were kept well sprayed throughout the season. 

 This is apparently due to the increased vegetative growth of 

 the sprayed plants, a fact which has been recorded by other 

 workers. 



The premature dropping of flowers as a result of the action 

 of known external conditions has already been mentioned. 

 But premature shedding of fruit also takes place as a result 

 of unknown causes, either internal or external. Thus M. J. 

 Dorsey (" A Note on the Dropping of Flowers in the Potato," 

 Journ. Heredity, 10, 226-28, 191 9) records that in many 

 varieties of the potato both buds and opened flowers fall in 

 large numbers. Although a large proportion of the pollen 

 grains abort, the absence of the stimulation of polhnation 

 cannot be cited as the reason for the dropping of the flowers, 



