i68 



A Cucumber Leaf Disease. 



Growers may have some difficulty in ascertaining whether it 

 is Cercospora, or Dendryphium, or both, that is present in their 

 houses, for the disease produced by the two fungi are rather 

 similar in appearance in their initial stages, but their later 

 development is quite different, and when once this difference is 

 appreciated it is an easy matter to distinguish between them. 



But quite apart from external appearances, the microscope 

 will settle the question absolutely, provided spores are present. 

 Dendryphium has minute oval spores, whilst those of Cercospora 

 are long and multiseptate, and about ten times as large as those 

 of Dendryphium. If it is wished to examine the spores, they 

 will be found on the velvety patches on the leaf spots, but should 

 there be any difficulty in obtaining them in situ they may be 

 readily procured by placing some infected leaves in a moist 

 chamber and leaving them for twenty-four hours ; a good crop 

 of conidiophores should then be visible on the spots, whether the 

 fungus be Cercospora or Dendryphium. 



The spores of Dendryphium when examined with the micro- 

 scope are small, oval, or cylindrical bodies, I — 2 septate at 

 maturity and nearly hyaline ; they vary considerably in size, 

 but the average is about 20 x 6/*. Fig. 5 shows the spores 

 magnified 400 times. (Fig. 7 is added by way of comparison to 

 show the difference in form and size of the spores of Cercospora.) 

 The spores are borne in simple or branched chains at the apex 

 of the hyphae, and are produced in enormous numbers. They 

 are capable of immediate germination, and artificial cultures 

 have been carried out in the laboratory showing that the fungus 

 is a true parasite. 



The hyphae, which are short and septate, are pale brown in 

 colour and 10/x in thickness. 



It is probable that Dendryphium possesses a higher form of 

 reproduction than that of the conidiospores just described, 

 though up to the present time efforts to discover anything like 

 a resting-spore stage have not been successful, but with a 

 number of artificial cultures still under observation it is hoped 

 that the other stage may be obtained. 



Preventive Measures. 

 It has been repeatedly observed that this disease (in common 



