ON THE VEGETATION OF DITCHAM PARK, HAMPSHIRE. 233 



(3) Light relations. — These have been specially studied so far in the 

 beech- woods. A first series of experiments has been carried out 

 during the season, which give interesting and striking results. 



The enclosed areas have been charted in detail, and also photographic 

 records have been taken from marked {wsitions. 



During the present season (1915) it has not been found possible to 

 carry out field experiments. 



The Committee ask to be reappointed, without a grant. 



Experimental Studies in the Physiology of Heredity. — Report 

 of the Committee , consisting of Professor F. F. Blackman 

 {Chairman), Mr. E. P. GtREGORY (Secretary), Professor W. 

 Bateson, and Professor F. Keeblb. 



Experimental work has been satisfactorily carried on during the past 

 year, and a summary of the results is given below. It is hoped that 

 it will be found possible to renew the grant, and thereby enable the 

 results to be carried further. 



Summary. 

 Experiments by E. P. Gregory and H. B. Killby. 



The investigations into the genetics and cytology of the tetraploid 

 races of Primula sinensis have been continued, and considerable progress 

 has been made in the recognition and testing of the three different 

 heterozygous types, AAAa, AAaa, and Aaaa. In cases where a single 

 dose of the factor is sufficient for the perfect development of the 

 character, these types can only be identified by the study of their 

 progeny; in self-fertilisation, the type AAAa gives no recessives among 

 its immediate progeny, but some of its offspring give recessives in the 

 next generation; the type AAaa gives the ratio 151) : IE ; while the type 

 Aaaa gives the familiar ratio 3:1. All these types have now been 

 identified experimentally. In the case of other factors the dominance 

 is not complete, and among these cases there are some, notably in 

 factors determining the shape of the leaf, the form of the corolla, and 

 certain colour-characters, in which the tetraploid races produce 

 heterozygous types unlike any types in the diploid races. The factorial 

 constitution of these peculiar types is being studied, and very satis- 

 factory progress has been made, especially in unravelling the complex of 

 factors which, between them, determine the coloration of the flower. 



It was hoped that a report on this part of the work would have been 

 ready for publication this summer, but circumstances connected with 

 the war have rendered delay unavoidable. 



The phenomena of coupling and repulsion have been studied further, 

 both in the diploid and in the tetraploid races. This work promises 

 most_ interesting results, "but has not yet progressed far enough to 

 permit of any definite statement as to new ground gained. 



