296 DISEASES OF CULTIVATED PLANTS 



elliptical, smooth, yellow, 20-26 x 16-22 p. Uredospores 

 forming sori of various sizes, often thickly scattered over the 

 entire under surface of the leaf, for some time covered by 

 the epidermis, elliptical, piriform, or rarely globose, orange 

 brown in the mass, with very delicate spines, or almost, or 

 quite smooth, 20-35x16-25 /*, sori of teleutospores dark 

 brown, scattered or in groups, piriform or elliptical, brown, 

 smooth, generally with a colourless papilla at the apex, 

 25-35 X 18-28 /A, pedicel hyaline, slender. 



As the ' tops ' of mangold more especially are utilised as 

 food for cattle, etc., it is difficult to convince the farmer that 

 a great risk is incurred when the leaves are diseased. It is 

 yet a more difficult task to induce him to collect and bury 

 all diseased leaves. If such are used for food, or put on 

 the manure heap, it is certain that many of the spores will 

 find their way back to the land uninjured. Nevertheless it 

 pays to do this, and do not plant the same kind of crop on 

 land that has produced diseased plants, for at least two years. 



Pea rust. This is caused by Uromyces pisi (De Bary). The 

 aecidium phase of the fungus (Accidium cyparissiae, D. C.) 

 grows on a spurge Euphorbia cyparissias. The mycelium 

 permeates every above-ground portion of its host-plant, 

 which becomes very much dwarfed in every part, and the 

 substance of the leaves is much thicker than in a normal 

 plant. The mycelium hibernates in the plant. The spermo- 

 gonia and aecidia are scattered over the entire surface of 

 the leaves. The uredo and teleutospore stages from reddish- 

 brown pustules on the leaves of the cultivated pea, also on 

 those of other leguminous plants, Vicia cracca^ V. tenuifolia^ 

 Lathy rus pratensiS) L. silvestris^ L. tuberosus, etc. 



The aecidia are whitish, spores subglobose or polygonal, 

 minutely warted, contents yellow. 



Uredospores more or less elliptical, rusty-brown, minutely 

 echinulate. 



Teleutospores almost globose, wall minutely punctate, 

 maroon-brown, apex thickened and with a colourless papilla, 

 pedicel slender. 



So far as this country is concerned, Euphorbia cyparissias 

 is not an indigenous plant, but as an introduction is sparsely 

 distributed. If this plant is removed from the neighbourhood 

 of peas, there can be no danger of infection. The fungus 

 has not been observed in England. 



