A UNIFOLIOLATE MUTATION 



IN THE ADZUKI BEAN 



A. F. Blakeslee 

 Station for Experimental Evolution, Cold Spring Harbor, Long Island, N. Y. 



THE Adzuki Bean (Phaseolus an- 

 gularis), like other members of 

 the genus Phaseolus to which our 

 common beans belong, is trifoli- 

 ate. Although the first pair of leaves 

 above the cotyledons are simple, those 

 later formed are regularly compound 

 each with three leaflets. Occasional 

 abnormalities in individual leaves, it is 

 true, may be found, and the writer has 

 record of a seedling plant with but a 

 single simple leaf which was unable 

 to continue growth on account of the 

 lack of buds. So far as the writer is 

 aware, however, a full-grown Adzuki 

 Bean plant with all its leaves simple has 

 only once been observed. In view of the 

 number of plants of this species that 

 have been under close observation for a 

 considerable length of time, it seems 

 worth while to make a brief record of 

 this occurrence. 



The plant on the right in Fig. 2 is 

 shown beside a normal individual from 

 the same pedigree. Unfortunately the 

 photograph was not taken till late in the 

 season when the foliage was in an imper- 

 fect condition. A typical unifoliolate 

 leaf isolated from this plant is shown on 

 the background at the right in contrast 

 with a typical trifoliate leaf on the 

 extreme left from the normal plant. 

 The mutant plant was somewhat taller 

 than its neighbors in the same pedigree, 

 was more branched and retained its 

 leaves longer. In fact it was difficult 

 when the photograph was taken to find 

 a normal plant that had not lost most of 

 its leaves. These peculiarities in habit 

 may be due to the fact that the plant 

 was entirely sterile, and vegetative 

 functions in consequence were not 

 checked by the production of fruit. 

 Buds were formed in densely packed 



spikes giving promise of abundant 

 flowers. No fully formed flowers, how- 

 ever, ever developed. The buds all 

 dropped at an early stage before the 

 petals were visible. As the dropping 

 proceeded from the base upwards, the 

 axis of the cluster progressively elon- 

 gated and thickened. These floral clus- 

 ters may be seen projecting from the 

 plant in many places. They show the 

 terminal clusters of young buds and the 

 elongated axes studded with warty 

 scars that mark the places from which 

 buds have fallen. 



The unifoliate plant was the only one 

 of its kind in a row of some 1,500 plants 

 grown in 1918. The parents of this 

 pedigree were the offspring of a single 

 select plant grown in 1918. The line 

 from which the mutant arose came from 

 a single plant grown in 1913. The 

 descendants of this original plant, in- 

 cluding a number of sublines, comprise 

 2,672 individually counted plants in 

 addition to about 4,700 plants not 

 actually counted although grown under 

 close inspection. It is safe to say, 

 therefore, that the mutant in question 

 was the only one of its kind in an inbred 

 line comprising around 7,400 individuals. 

 Moreover, no unifoliolate plant has been 

 observed in rather extensive plantings of 

 Adzuki Beans of various other lines. In 

 1917 all the plants in the field, number- 

 ing 42,174 individuals, were under close 

 observation and frequent records were 

 taken of them in regard to time of 

 flowering and maturity of pods. In 

 1918, select pedigrees comprising around 

 74,100 individuals were likewise repeat- 

 edly inspected for flowering and matu- 

 rity. All the plants grown in the field in 

 1917 and the select pedigrees of 1918 

 were so frequently inspected that it 



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