THE COWPEA FLOWER AND ITS POLLINATION. 25 



respect to the heredity of the 4-leaved and 5-leaved clover plants as 

 determined by De Yries. 



A rare malformation of the leaves among cowpeas is the forma- 

 tion of pitchers or ascidia. Some illustrations of these curious 

 growths are shown in Plate VIII. 



SUSCEPTIBILITY AND RESISTANCE TO DISEASES. 



The cowpea is affected by a considerable number of diseases, the 

 most common being wilt (Neoeosmospora vasinfecta var. nivea Erw. 

 Sm.) ; root-knot caused by the nematode worm (Heterodera radici- 

 cola (Greef) Mull.) ; rust (Uromyces phaseoli) ; white leaf -spot 

 (Amerosporium economicwn) ; red leaf -spot (Cercospora cruenta) ; 

 and mildew (Sphaerotheca sp.). Root-knot and wilt are so common 

 throughout much of the cotton belt that most cowpea varieties suffer 

 serious damage. The Iron variety and some recently bred hybrids 

 of Iron are completely resistant to these diseases, and only such 

 should be grown where these diseases prevail. (See Webber and 

 Orton, Bulletin 17, Bureau of Plant Industry, United States Depart- 

 ment of Agriculture.) 



Rust is a disease to which most standard American varieties of 

 cowpeas are immune. Many recently imported varieties, especially 

 from China and India, are, however, very susceptible to this disease 

 and suffer severe injuries from it. That other varieties are com- 

 pletely immune to rust would appear from the fact that they are 

 never affected even when growing contiguous to a rusted variety on 

 the same ground for several years in succession, which has been the 

 experience at Arlington Farm. This disease was very much in 

 evidence at Arlington in 1908 and 1909, but was entirely absent in 

 1910. 



The two leaf-spot diseases are very common and most varieties of 

 cowpeas are subject to one or the other of them — many, indeed, being 

 affected by both. The most serious apparent result is the early fall- 

 ing of the leaves, or in very susceptible varieties their almost com- 

 plete destruction. The best varieties are but little affected by these 

 diseases, but it is doubtful if any variety is completely immune. 



In general, cowpeas display a great range of susceptibility and 

 resistance to the various diseases to which they are subject. Among 

 the best varieties there is great or even complete resistance to all the 

 more serious of these diseases, so that any serious loss from this source 

 can probably be obviated by breeding. 



THE COWPEA FLOWER AND ITS POLLINATION. 



The flowers of all the cultivated vignas are practically identical. 

 They are borne in pairs in a short spike at the end of a stout 

 peduncle, the pairs alternately arranged. From 1 to 12 closely 



229 



