48 Inheritaiice in Pisum 



year, partly by gametic constitution and partly by the external condi- 

 tions to which the plants are subjected during their growing period. 

 Thus the two half-dwarf varieties Autocrat and Bountiful, used in our 

 experiments, are so constant with respect to stature as to be described 

 by Messrs Sutton and Sons, to whom we are indebted for seeds, as 

 being, the former variety 8 — 4 feet, the latter '?>\ — 4 feet in height. 

 Nevertheless, during the constantly wet summer of 1909 both Autocrat 

 and Bountiful reached in the College Gardens at Reading an average 

 height of 5 — 6 feet. We refer to these well-known seasonal fluctuations* 

 in height in order to point out that particular care is required in the 

 interpretation of the results obtained in any one year and in the 

 comparison of the statures of plants grown during different years. 



The cross Autocrat and Bountiful and its reciprocal. This cross, 

 made in 1907, and repeated in 1908, yielded an F^ generation, the 

 plants comprising which were considerably taller than either parent 

 grown under like conditions. The average height of F^ plants was 

 7 — 8 feet, that of the parent plants 5 — 6 feet. 



jPi selfed, yielded offspring {F^ which ranged in height from 8 feet 

 down to 1^ feet. In all, 192 F^ plants were recorded. Of this number, 

 61 plants were the progeny of a single F^ plant of Autocrat x Bountiful 

 grown in 1908. The remaining 131 plants of the F^ generation were 

 descended from four F^ plants of the cross Bountiful x Autocrat. 

 The seeds from these four plants were, owing to a mistake, harvested 

 together. There is, however, no recognisable difference between the 

 descendants of the single family from Autocrat x Bountiful and those 

 derived from the four F^ plants of Bountiful x Autocrat. We will 

 therefore consider the 192 F^ plants as a whole. 



The F2 plants, showing such marked differences among themselves 

 with respect to height, fall into four groups which, for the moment, 

 may be defined as follows: — F^ type, Autocrat type, Bountiful type, 

 and Dwarf type. Moreover, when classified in this way, the numbers 

 of plants in the four groups show a close approximation to those 

 expected in the F^ generation derived from a dihybrid cross; that is 

 one in which two pairs of characters are involved. 

 Thus : ¥2= 



Inspection of the parent plants. Autocrat and Bountiful, reveals the 

 fact that, besides other, apparently minor, differentiating characters, 



