y6 
wholly on one host plant, altogether omit some of the 
spore forms from the life story. _ Whilst showing these 
variations, however, the rust fungi are all highly 
specialised parasites; they cannot grow apart from living 
plants, and with rare exceptions, a specific rust fungus is 
restricted to a single species of piant. 
Further information on the subject of diseases of 
plants caused by parasitic fungi may be obtained from 
the following books :—- 
Ward, H. M. “ Diseases of Plants,” S.P.C.K., London. 
Duggar, B. M. “ Fungous Diseases of Plants,” 1909, Ginn and 
Company. 
Massee, G. “ Diseases of Cultivated Plants and Trees,” Duck- 
worth, 1910. 
