28 ORCHARD GREEN-MANURE GROPS IN CALIFORNIA. 
during the cool weather of the winter, thus affording a heavier growth 
to be turned under. This is an especially strong point where it is 
desirable to turn the crop under as early as possible, as is the case in 
the citrus orchards of southern California. The plants referred to 
are the black-purple vetch, the black bitter vetch, the woolly-podded 
vetch, the horse bean, and the Tangier pea. 
BLACK-PURPLE VETCH. 
The black-purple vetch (Vicia atropurpurea) is one of the most 
promising green-manure crops tested for California. Its general 
Fic. 7.—A field of black-purple vetch at Chico, Cal. 
appearance and habit of growth are about like those of the com- 
mon vetch (fig. 7), although it is very distinct from that species. 
The superior value of black-purple vetch when compared with com- 
mon vetch lies in its ability to make a much stronger growth during 
the cool weather of early winter. This, as noted elsewhere, is an 
especially desirable quality in a green manure to be turned under in 
February. 
The root system of black-purple vetch, which is similar to that of 
common vetch, is well covered with medium large nodules. The 
stems, aside from making a strong growth, are of such a texture as 
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