THE FUNGI 217 



are near relations of normal chlorophyll - containing 

 plants, and we attach no great systematic importance 

 to the change in their mode of life. Among Fungi, on the 

 other hand, there seems to be a real bond of relationship 

 throughout the entire class (if we leave a few doubtful 

 cases out of consideration) so here it is probable that 

 the common physiological character coincides with a 

 common origin. We must not, however, suppose that 

 all Thallophyta, which lead the life of parasites or 

 saprophytes, are necessarily Fungi. At the close of this 

 book we shall have to consider two such Families which 

 cannot be classed under this head. 



Many Fungi are of the greatest practical interest, 

 though chiefly in a disagreeable way. Very many of 

 them are destructive parasites, causing the worst 

 diseases of our field and garden crops and of forest 

 trees. We may mention the rust, smut, and bunt of 

 wheat, the potato disease, the sugar-cane disease, the 

 larch disease, to which innumerable others might be 

 added. Others do harm by injuring timber in buildings, 

 such as the dry-rot fungus, or by destroying articles of 

 food, which are constantly attacked by " mould." Hence, 

 Fungi have been more studied from a practical point of 

 view than any other Cryptogams, and a vast mass of 

 knowledge has now been accumulated as to their 

 physiology and mode of life. Our own point of view is 

 chiefly a morphological one, and we have chosen the 

 few types which we have space to describe, in order to 

 illustrate some of the most striking facts in the com- 

 parative structure and life-history of certain of the more 

 important Families. 



It must not be supposed that Fungi are altogether to 

 be regarded as injurious to the higher creatures. Not to 



