266 IOWA ACADEMY OF SCIENCE Vol. XXV, 191S 



5. The period covering the time during which the different 

 trees formed and developed their flowers extended from about 

 the first of July, 1916, to May 17, 1917, thus being about ten 

 months in length. 



6. Apple flowers have two periods of rapid growth. The first 

 one immediately follows the differentiation of the flower bud 

 from the leaf bud, and during this period, »vhich is about six 

 weeks in length, the floral organs are differentiated. During the 

 second period, which begins about six weeks previous to the 

 opening and ends with the full expansion of the flower, the 

 floral organs increase their size many times. During the time 

 intervening between the two periods of rapic growth, growth 

 continues but is slow. 



INTRODUCTION. 



This series of apple fruit bud iuA^estigations was started as 

 graduate work under the direction of the semor author by F. 

 M. Harrington of tlie Horticultural staff at the suggestion of S. 

 A. Beach, Chief in Horticulture of the Iowa Experiment Sta- 

 tion. The collection of material for this purpose was begmi by 

 T. J. Maney, now Chief of Pomology of the Station. Later 

 the work passed into the hands of the junior aathor, R. S. Kirby, 

 as a fellow in horticulture. 



These investigations were inaugurated as a phase of the or- 

 chard hunms project w^hicli is being carried on by the Pomology- 

 Section with the co-operation of the Soils Section of the station. 

 This project was inaugurated in 1910 in an orchard near Coun- 

 cil Bluffs which has been leased till 1925 for this purpose. It 

 was initiated by and has remained under the general supervision 

 of Professor Beach with the immediate management in charge of 

 Chief Laurenz Greene for the horticultural staff. In 1917 Chief 

 ]\Ianey succeeded Professor Greene in this w^ork. 



This orchard humus investigation is a modified continuation 

 of the orchard humus project initiated by Professor Beach at 

 the State Experiment Station, Geneva, New York, in 1903 and 

 carried forward by him for three years befo*e coming to Iowa. 

 The results of that work have been reported by Hedrick (17) in 

 New York Station bulletins 314 (1909), 375 (1914). and 376, 

 (1914), and in otlier publications. 



Owing to the close relation between the formation of flowers 

 and the production of fruits, a good knowledge of the factors af- 

 fecting the development of fruit 1)uds is essential to a scientific 



