422 



BOTANY OF CROP PLANTS 



numerous ovules. Members of the genus are quite regularly 

 visited by insects. The pod is linear, straight or curved, 

 subterete or compressed, two-valved, and tipped with a 



persistent style. The seeds 

 ("beans") are large and 

 have a prominent, approx- 

 imately central hilum, on 

 one side of which is the 

 micropyle, on the other, 

 the raphe. The embryo is 

 large and occupies the 

 whole of the seed, i.e., 

 endosperm is wanting. 

 The hypocotyl and 

 plumule are prominent; 

 the two large cotyledons 

 are slightly concave on 

 their inner faces. The 

 germination of the bean, 

 and the bean seedhng, are 

 common objects of study 

 in general botanical 

 courses. 



Geographical and Species. — 



Members of the genus Phaseolus 

 are tropical and warm-country 

 plants. According to Britton and 

 Brown, there are close to i8o 



Fig. 176. — Common kidney bean 

 (Phaseolus vulgaris). A, spiral keel; B, 

 entire flower. X 2j^. 



species. 



A number of "beans" do not 

 fall within the genus Phaseolus, for example, broad bean {Vicia faba), soy 

 bean (Soja max), velvet bean (Mucuna utilis), asparagus or dolichos bean 

 {Vigna sesquipedalis) , cowpea or bean {Vigna sinensis),'' ]ack bean (Cana- 

 valia ensiformis), locust bean {Ceratonia siligna) and hyacinth bean, bonavist 

 or lablab {Dolichos lablab). 



