252 INTRODUCTION TO THE STUDY OF FUNGI 



attack growing plants, and produce copious soot-like spores, so 

 that they have acquired the general name of " Smuts." The 

 mycelium is deeply seated in the tissues, and the spores are 

 developed in definite positions on the host : on the stem, 

 leaves, flowers, ovaries, fruit, and sometimes in the corm, tuber, 

 or root, but seldom in more than one of these places, and that 

 one habitual to the species. A good example may be seen in 

 the smutted ears of corn, or the distorted receptacles of the- 

 goat's-beard. 



The mycelium is an important element in this family, 

 although so delicate and deeply seated that it is often passed 

 over. The whole substance of the host may be penetrated 

 and taken possession of by the mycelium before there is any 

 external evidence of its presence ; therefore when the pustules 

 are formed it is too late to apply remedial measures, for the 

 plant has long been doomed. It is always tedious and difficult 

 to trace the ramifications of mycelium in growing tissue, but 

 in some of these species it may be seen bearing haustoria or 

 suckers amongst the cells. Not only does the mycelium 

 traverse the intercellular spaces, but frequently the branches 

 pierce the walls of the cells, and though seen most readily in 

 young plants, it is always manifest about the spore-pustules. 

 The persistency of the mycelium is one of the agencies by 

 which the continuity of the species is preserved. When the 

 foster-plant dies in the winter the mycelium dies with it, but 

 when the root-stock is perennial the mycelium also remains, 

 to revive and penetrate the young shoots which are put forth 

 in the spring. All the leaves of the violet may die year after 

 year, and still every season Urocystis violae appears again, even 

 when every infested leaf has been picked and burnt. 



The most important function of the mycelium in this 

 family is its concern in the formation of the fruit. At the 

 special spot where the development of fructification is to take 

 place the mycelium undergoes some change in its character : the 

 walls increase in thickness, and the contents become gelatinised. 

 Some slight modifications take place in the different genera, 

 but for the most part the hyphae branch and become en- 

 tangled so as to form compact knots, or spore -beds. With 

 this the hyphae gradually swell in places, and it is evident 



