SYSTEMATIC BOTANY OF BEANS, AND THEIR ALLIES 



15 



and Bruner (Root Development of Vegetable Crops 

 184 ff. 1927^. The strain of nitrogen-fixing bacteria 

 on bean roots seems to be specific for Phaseolus. 



The leaves vary in color from light green to dark 

 green in different varieties and there seems to be some 

 correlation between depth of seed coat color and dark- 

 ness of leaves. 



The flowers are showy, white, purplish, or yellowish 

 and are borne in closely aggregated clusters on the ends 

 of short peduncles. The inflorescences of the pole beans 

 appear continually during the season, due to the inde- 

 terminate habit of the stem, and flowers and fruits in 

 all stages of development may be found on a plant at 

 the same time. On the bush beans, however, due to 

 the determinate growth of the stem, the flowers appear 

 almost simultaneously and the fruits mature together. 

 The corolla is of the typical " butterfly " type. The 

 upper petal or standard is large and bends sharply 

 backward. The lateral petals or wings extend forward 

 and are considerably longer than the standard. The 

 two lower petals form the keel which in this genus is 

 spirally coiled at the tip. The stamens and style are 

 included within the keel and the end of the style is 

 coiled in the same manner as the tip of the keel. 



Due to this peculiar infolding and coiling of the 

 lower petals, the flower presents considerable hindrance 

 to cross-pollination by insects, though bees and some 

 other insects do succeed in pollinating a small propor- 

 tion of bean flowers. Emerson (1. c.) found from 

 to 10 per cent of crossing in lines with which he was 

 working and Kristofferson iHereditas 2:395—400. 1921) 

 found 0.19 per cent in green-shelled varieties, 0.8 per 

 cent in snap beans, and 1.42 per cent in dry field beans. 

 Many varieties showed no crosses. Self pollination 

 occurs readily. Pollen grains may begin to germinate 

 4 or 5 hours before pollination actually occurs, according 

 to Weinstein (Am. Jour. Bot. 13:248. 1926), and 

 the tube enters the micropyle of the ovule within 8 or 

 9 hours after pollination. The chromosome number of 

 the varieties thus far examined is n=ll. 



The inheritance of color in the bean flower has been 

 studied by Shaw [Massachusetts Agr. Exp. Sta. 

 Bulletin 25 1-24. 1913.) and three types of color, 

 carmine red, rose, and white differentiated. Rose and 

 light rose seem to behave alike, but there may be two 

 factors involved in white. Pending further investiga- 

 tions, however, it may be said that of the colors given 

 carmine red is dominant over either of the others and 

 rose is dominant over white, both apparently in a straight 

 3:1 ratio. 



The fruit of beans is a typical legume, a pod with a 

 single cavity opening along both dorsal and ventral 



sutures when dry. Unlike peas, the calyx is not per- 

 sistent, though the base of the style forms a sharp tip 

 to the pod. Various pod characters have been studied 

 genetically. Green color is dominant over yellow in the 

 unripe pod in straight Mendelian ratio (*); round 

 shape is likewise dominant over flat (*) ; blunt apex 

 over sharp ( 3 ); non-constricted over constricted 

 threshable over non-threshable (*); irregular segregation 

 was found in the results of crossing broad-podded forms 

 and narrow-podded ones ('"<, and long-podded and short- 

 podded forms i : i , though parchmented forms were found 

 to be purely recessive when crossed with non-parch- 

 mented types. 



The seeds are borne alternately on the two placentae 

 bordering the ventral suture. There is a wide variation 

 in color, size, and shape of the seeds; and although there 

 have been numerous genetic studies of the factors 

 involved, the results are so complicated as to render 

 attempts at generalizations useless. This study is 

 further complicated by the fact that the shade of color 

 of the seed coats is liable to change in storage. 



Selection of improved types has been the type of 

 breeding work of most practical value thus far. Johann- 

 sen (Uber Erblichkeit in populationem und in 

 reinen Linien Jena, 1903; has shown that pure lines 

 are very generally stable and mutations occur very 

 rarely. 



Beans are subject to several diseases in this State, 

 blight (Bacterium phaseoli) , wilt (B. flaccumfaciens) , 

 anthracnose (Colletotrichum lindemuthianum), 

 rust (Uromyces appendiculatus) , root rot iFusarium 

 spp.), and mosaic being the chief maladies. The bean 

 weevil and the Mexican bean beetle are the chief insect 

 pests. 



9. Phaseolus lunatus L. Sp. PI. 724. 1753. 

 Lima Bean. — P. inamoenus L. Sp. PL 724. 1753. 

 P. rufus Jacq. Hort. Vindob. 1:13. 1770. P. 

 bipunctatus Jacq. 1. c. 144. P. tunkinensis Lour. 

 Fl. Cochinch. 435. 1790. P. macrocarpus Moench. 

 Meth. 155. 1794. P. Xuarezii Zucc. in Roem. 

 Collect. 4:149. 1809. P. saccharatus Stokes Bot. 

 Mat. Med. 4:16. 1812. P. parviflorus Stokes /. c. 

 4:18. 1812. P. macrocarpus Poir. Encycl. Suppl. 

 3:6. 1813. P. derasus Schrank, PL Rar. Hort. 

 Monac. 89. 1819. P. puberulus H. B. K. Nov. Gen. 

 & Sp. 6:451. 1823. P. maximus Roxb. Fl. Ind. 

 3:288. 1832. P. ilocanus Blanco Fl. Filip 572. 1837. 

 P. vexillatus Blanco 1. c. 2 74. P. dumosus Macf. 

 FL Jam. 1. 279. 1837. P. limensis Macf. /. c. 

 P. foecundus Macf. /. c. 281. P. latisiliquus Macf. 

 /. c. 282. P. saccharatus Macf. /. c. 282. P. platy- 

 spermus Haberle in Steud. Nom. erf. 2. 2: 17. 1841. 



(>) Emerson, Mass. Agr. Exp. Sta. Bulletin 25 1-24. 1913: Lock, Ann. Roy. Bot. Gard. 3:95ff. 1906: and Tschermak, Zeits. 

 Pflanz. Zucht. l:65ff. 1916. 



Tschermak, /. c. 



Tschermak, /. c. and Zeits. Abst. u. Vererb. 28:28ff. 1922. 

 («) Tjebbes & Kooiman, Genetics 4:447ff. 1922. 

 ( 5 j Emerson /. c. 

 («) Tschermak /. c. 

 P) Emerson /. c. ; Tschermak /. c. . and Wellensick, Genetica 4:443ff. 1922. 



