15 



CULTURES. 



Microscopical oxaiiiiiiation alone is of course not sufficient to abso- 

 lutely settle a point of the kind in question. The tissues must be 

 carefully examined according- to the ])est culture methods. After 

 many trials in washing- and flaming- the leaf it was found that it was 

 impossible, as before stated, to free the cuticular portion xrom sap- 

 rophytic organisms without heating the leaf to such an extent that 



Fig. 2. —Cross .sectiuu of n, carnation leaf several days after it had been punctured by an aphid. 

 The proteid sheaths between the cells mark the line of puncture. The cells on both sides have 

 become abnormally large. (Drawn with Zeiss camera lucida, x 2-18 diameters.) 



internal forms would also be destroyed. In cases where heating h'.id 

 not been continued long enough to kill the epidermal cells, surface 

 cultures of the cuticle of flamed leaves often developed both molds 

 and bacteria. Cultures were therefore made from the diseased meso- 

 phyll direct by carefully peeling off the epidermis of the leaf and 

 scraping out the inner tissues with a flamed scraper which had been 

 allowed to become perfectly cool. After the removal of the epidermis 



