50 MICROSCOPIC FUNGI. 



mycelium^ penetrate the intercellular spaces^ and 

 insinuate themselves in a complete network^ amongst 

 the cells of which the leaf, or other diseased portion 

 of the plant_, 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 whole 

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

 vegetative system of one fungal plant. At first 

 this mycelium might have originated in a number 

 of individuals^ which afterwards became confluent 

 and combined into one for the production of fruity 

 that is to say_, an indefinite number of points in the 

 vicinity of the future mycelium developed threads ; 

 and these^ in the process of growth^ interlaced each 

 other^ and ultimately^ by means of transverse pro- 

 cesses^ became united into one veg'etative 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 

 consequence of this increase in bulk^ the cuticle 

 becomes distended in the form of a pustule over the 

 yellow cellules^ and at lengthy unable longer to 

 withstand the pressure from beneath^ ruptures in 

 irregular^ more or less elongated fissures (plate VII. 



