F. Keeble 175 



the outset that the method by which the following records were 

 made — that of appraising gigantism by reference to the gross ap- 

 pearances presented by individuals — is open to grave objections. For 

 example, a large and massive flower may, if seen among a family of 

 small-flowered plants, be classed unhesitatingly as a g^ant, although 

 if it were judged side by side with indubitable giants, it might be 

 relegated to the class of doubtful or semi-giants. 



On the other hand an observer who spends a considerable amount 

 of time among plants of a certain kind gains in some measure a 

 sureness of judgment with respect to the " points " of those plants 

 which is not likely to lead him into very serious errors of observation. 



In spite of the drawbacks of the method of classification which 

 has perforce been adopted in these experiments, the results which 

 have been obtained appear to be worth recording both for their 

 inherent interest and for the purpose of demonstrating that the 

 phenomena of gigantism presented by P. sinensis are less simple than 

 those exhibited by other plants which have been the subject of like 

 investigation. 



For example, the genetics of the gigantism of sweet peas (Bateson, 

 1909 a) and of culinary peas (Keeble and Pellew, 1910) is of a fairly 

 simple kind. Thus in Pisum sativum gigantism depends for its ex- 

 pression on the presence of two factors.* Of these growth-factors, the 

 one induces excess of growth in length (factor for long intemode), 

 the other induces excess of growth in thickness (factor for thick 

 intemode). 



In the presence of both these factors, either in a pure or hetero- 

 zygous state, the plant is a giant (6 ft.), in the absence of either it 

 is of mid-stature (3 — 4 ft.), and in the absence of both it is a dwarf 



(1-H ft.). 



The gigantism of P. sinensis is built on less simple Mendelian 

 lines. 



The experiments which lead to this conclusion, recorded in 

 Tables IV, V, and VI, were made mainly at University College, 

 Reading; though some records which are included in the tables are 

 those of breeding-experiments carried out by Messrs Sutton and Sons 

 at their trial grounds. The records derived from the latter source 

 are indicated in the tables; those in which the source is either not 

 mentioned or indicated by the letters U. C. R. were carried out at 

 University College. 



For access to the records of Messrs Sutton and Sons' experiments 



