220 SCIENCE PROGRESS 



as this takes place in many cases before pollination would 

 normally be effected. 



The same author has made a study of the shedding of flowers 

 and young fruit in the plum {Genetics, 4, 417-488, 191 9). He 

 comes to the conclusion that there are three distinct periods 

 in which shedding of the flowers or immature fruits takes 

 place. The first period occurs very shortly after flowering. 

 Investigation of the fallen flowers shows that these contain 

 defective gynaecia, and it must be concluded that this shedding 

 of flowers is connected with the presence of the functionless 

 gynaecia. A similar phenomenon has been observed in apricot 

 trees and some varieties of plum growing in the neighbourhood 

 of Vienna by J. Loschnig (" Die Verkiimmerung der Apriko- 

 senblute," Zeitsch. /. Garten- u. Obstbau, 1, 27-28, 1920), who 

 concludes that the flowers exhibited starvation phenomena, 

 the origin of which the author thinks is to be found in a shortage 

 of phosphate in the soil. 



The second period of premature fruit shedding occurs, 

 according to Dorsey, about a fortnight after the first shedding. 

 In this second series of prematurely shed gynascia, the latter 

 are normal, but apparently fertilisation has not taken place, 

 either on account of the absence of pollination, or because 

 pollen tube growth has been too slow. A third shedding of 

 gynaecia or young fruits takes place later in which fertilisa- 

 tion has occurred, but growth of the embryo has become 

 arrested. 



Similar phenomena with regard to shedding of flowers and 

 fruits occur in other species, as, for example, the cherry and 

 some varieties of apple and pear, but other species show quite 

 distinct relations with regard to premature shedding. 



A number of investigations have been made during the last 

 few years on the chemical changes taking place in fruits during 

 ripening. Apples and pears have been investigated by E. L. 

 Overholser and R. H. Taylor (" Ripening of Pears and Apples 

 as Modified by Extreme Temperatures," Bot. Gaz., 69, 273-96, 

 1920), who find that in apples the rate of ripening is greater 

 the higher the temperature, but that with Bartlett pears there 

 is a definite retardation of the rate of ripening at temperatures 

 of 30° C. and over. This retardation reaches a maximum at 

 some temperature between 34-4° and 40°, at temperatures 

 above this ripening proceeding more rapidly. Pears ripened 

 above 30° C. are more acid and less sweet than those ripened 

 at lower temperatures. J. R. Magness (" Investigations in the 

 Ripening and Storage of Bartlett Pears," Journ. Agric. Res., 

 19, 473-500, 1920) also found that this same fruit kept at 

 30° F. had a lower acid content than that kept at 40° or 70° F. 

 He also found more sugar present in pears stored at 30° than 



