MOULDS, RUSTS, ETC. 119 



undergo such modifications of form and structure as to 

 result in the production of what was formerly thought to 

 be a distinct form of plant life ; namely, a lichen. The arti- 

 ficial production of lichens, however, by bringing about the 

 union of the appropriate fungus and alga, has been suc- 

 cessfully accomplished, and this, in connection with other 

 experimental proof, has established beyond all doubt the 

 compound nature of this large and extraordinary group of 

 organisms. 



The study of fungi has been so developed during the 

 last few years that a special and extensive literature has 

 grown up, to which students interested in the subject are 

 referred. There is no department of botany embracing 

 more difficult and at the same time more fascinating prob- 

 lems, nor in which, in spite of obstacles, more progress is 

 being made. Its scientific and economic importance are 

 now so fully recognized that investigation is provided for 

 by the general government and by the experiment sta- 

 tions of many states, with results that already amply 

 justify what has been done. 



