126 MICROSCOPIC FUNGI. 



these appendages are always present^ it is easy to 

 discover the mycelium wherever it exists amongst 

 the tissues of an affected plant. 



The white pustules already alluded to contain the 

 fruit of the parasite. Bundles of clavate or club- 

 shaped tubes are produced upon the mycelium be- 

 neath the epidermis of the infested plants forming 

 a little tuft or cushion^ with each tube producing 

 at its apex reproductive cells,, designated ^^ conidia.''^ 

 These conidia appear to be produced in the follow- 

 ing manner : — -The tips of the clavate tubes gene- 

 rate them in succession. At first a septum^ or 

 partition^ divides from the lower portion of the 

 tube a conidium cell ; this becomes constricted at 

 the septum and assumes a spherical shape^ at 

 length only^ attached by a short narrow neck. 

 Beneath this again the same process is repeated 

 to form another and another conidium in succession^ 

 until a bead-like string of conidia surmount each 

 of the tubes from which they are produced (plate 

 X. fig. 200). At length the distended epidermis 

 above is no longer able to bear the pressure of the 

 mass of engendered conidia within^ and is ruptured 

 irregularly^ so that the conidia^ easily separating 

 from each other at the narrow neck^ make their 

 escape. 



As long since as 1807^ M. Prevost described the 

 zoospores^ or moving spores^ of these conidia^ and 

 his observations were confirmed by Dr. de Bary three 

 years since^ and are now adverted to by him again 



