4 INTRODUCTION TO THE STUDY OF FUNGI 



smuts and rusts which are so destructive to crops. There are 

 often to be seen discoloured spots upon living leaves which 

 cannot be attributed either to insects or Fungi. It is a common 

 mistake with novices to infer that all leaf spots are necessarily 

 caused by parasitic Fungi. Again, all the fixed or vegetable 

 parasites on insects are Fungi, whether moulds or the larger 

 club-shaped species of Cordyceps. Another caution becomes 

 necessary lest the pollinidia of Orchids, which are sometimes 

 seen temporarily attached to living insects, should be con- 

 founded with true parasites. Putrescent vegetable, and some- 

 times animal substances, give rise to Fungi, but dead wood and 

 the bark of trees may also support Lichens as well as the 

 living bark, on which Fungi are rarely found, except in cases of 

 incipient decay. No difficulty need be anticipated in respect to 

 Thallophytes found growing upon the ground, inasmuch as the 

 Lichens which have a terrestrial habit would scarcely be con- 

 founded with Fungi at any time, but especially after the 

 perusal of succeeding chapters on the details of structure in 

 the several orders. It should be understood that the above- 

 named distinctions are not so much of scientific value as they 

 may be useful as guides to collectors. 



The mycelium of Fungi is so general, although at times 

 nearly obsolete, tliat it must be regarded as somewhat analogous 

 to the thallus of Lichens, but not to be confounded therewith. 

 In the Agarics this mycelium is commonly termed the 

 " spawn," and consists of delicate threads, which traverse the 

 soil or the rotten wood upon which the Fungus is grown. In 

 some instances a strong mycelium is developed, but no perfect 

 Fungus is produced upon it. An instance may be found in the 

 substance called Xylostroma giganteum, which forms thick sheets 

 like leather, destructive of wood of solid texture. It is doubt- 

 less a degraded form of wood-destroying Hymenomycete.^ The 

 moulds and the mucors produce at first decumbent barren 

 threads, which constitute the mycelium out of which sub- 

 sequently the fertile threads arise. In the " rusts " or Uredines 

 the cushion-like base of the pustules is surrounded by the 

 delicate threads of mycelium. Going back to its origin, we 

 discover that the initial spore, or spores, upon germination pro- 



^ See next cliapter, p. 10. 



