418 I'ROTKCTION AOAINST PLANTS. 



years, as seeds of the dodder may remain 2 and 3 years 

 dormant in the ground. Hares spread the infection by 

 swallowing the seeds and passing them undigested on to the 

 ground. 



As dodder spreads from forest plants, and hedgerows where 

 it is very frequent, to crops, its destruction is urgent from 

 motives of general utility. 



7. Forest Weeds acting as Hosts for Injurious Fungi. 



The common barberry {Dcrheris vulgaris, L.) is a shrub 

 widely spread over Europe, both in the lowlands and moun- 

 tains, and generally along the edges of forests. It grows 

 even on poor sandy soil, soon attains a height of 12 feet, and 

 sends out its deep root-system in all directions. Barberry is 

 very hurtful as the host of black-rust {Puccinia graminis, 

 Pers.) that attacks wheat and other cereals, and should there- 

 fore never be used to form hedges. Its use for this purpose 

 has been prohibited in Prussia since 1880. 



Puccinia graminis, Pers., forms yellow lines of sporangia 

 on the blade of wheat and other grasses which afterwards 

 become reddish-brown, and in this way the nourishment of the 

 plants attacked is intercepted and the crop reduced. It lives 

 alternately in the form known as Aecidium Ik'rheridis, Pers., 

 on species of Berheris, or Mahonia, the spores of which falling 

 on cereals and other grasses hibernate as P. graminis, the 

 spores from which re-infect the barberry and so on. Another 

 form, crown-rust, P. coronata, Corda., which also forms a 

 rust on cereals, and especially on oats, arises from Aecidia 

 that form golden-yellow swellings on Ehamnus catharticus 

 and It. Frangida, the two species of buckthorn already 

 described. 



Species of Udn's are the hosts of Cronartium ribirolum, 

 Dietr., which produces Weymouth Pine blister {Peridermiuni 

 Strohi, Kleb.). 



Species of Senecio harbour Colcospori^nn Senccionis, Fr., 

 which alternates in the form of Peridermiuni Pini acicola, 

 Pers. (p. 461), a fungus attacking the needles of Scots and 

 other pines, and described further on. Species of Coleosporium 



