60 MICROSCOPIC FUNGI. 



mycelium^ penetrate tlie interceUular spaces^ and 

 insinuate themselves in a complete network^ amongst 

 tlie cells of whicli tlie leaf, or other diseased portion 

 of the plantj is composed. High powers of the 

 microscope^ and equally high powers of patience 

 and perseverance,, are necessary to make out this 

 part of the structure. We may regard the wholo 

 mycehum of one pustule^ or spore-spot^ as the 

 vegetative system of one fungal plant. At first 

 this mycehum might have originated in a number 

 of individuals^ which afterwards became confluent 

 and combined into one for the production of fruit, 

 that is to say^ an indefinite number of poiuts in the 

 vicinity of the future mycehum developed threads ; 

 and these^ in the process of growth^ interlaced each 

 other^ and ultimately^ by means of transverse pro- 

 cesseSj became united into one vegetative system^ 

 in which the individuality of each of the elementary 

 threads became absorbed^ and by one combined 

 effort a spore-spot^ or cluster of fruity was produced. 

 In the first instance a number of minute^ trans- 

 parent^ colourless cellules are developed from the 

 mycelium : these enlarge^ become filled with an 

 orange-coloured endochrome, and appear beneath 

 the cuticle of the leaf as yellowish spots. As a 

 conseqxience of this increase in bulk^ the cuticle 

 becomes distended in the form of a pustule over the 

 yellow cellules^ and at lengthy unable longer ta 

 withstand the pressm^e from beneath^ ruptures in 

 irregular^ more or less elongated fissures (plate YII. 



