1 88 DISEASE IN PLANTS. 



commonly indicate the presence of Uredineae, and 

 sections under the microscope will show the 

 mycelium in the tissues beneath. Species of 

 Uroinj'ces, Puccinia, etc., in the Uredo state have 

 the spots powdery with spores ; Aecidia show the 

 characteristic " cluster cups," and so forth. These 

 spots are often slightly pustular, and in some cases 

 markedly so. 



Other fungi also induce yellow spots on leaves 

 e.g. Phyllosticta on Beans, Exoascus on Poplars, 

 Clasterosporium on Apricot leaves, Synchytriuni 

 Succisae on Centaurea, etc. 



Yellow spots are also a frequent symptom of the 

 presence of Aphides, of Red Spider, etc. Thus the 

 minute golden yellow spots sometimes crowded on 

 Oak leaves are due to Phylloxera punctures. 



Yellow patches are formed on the large leaves 

 of A risaruvi by a species of parasitic Alga, Phyllo- 

 siphon, which lives in the mesophyll. Many 

 tropical leaves are spotted yellow by epiphytic 

 Algae e.g. CepJialeuros. 



It must be noticed that many fungi produce 

 yellow spots or flecks in the earlier stages, which 

 turn brown or black as the fructifications appear, 

 e.g. DilopJiia graininis, Rliytisnia acerinuni. 



The yellow-spotted leaves of Farfugimn grande 

 {Senecio Kaempferi) are so like those of Petasites 

 attacked with Aecidium in its early stages, that an 

 expert might be deceived until the microscopic 

 analysis was completed. 



Red spots, varying from rusty or foxy red to 

 bright crimson, are the symptomatic accompaniment 



