INTRODUCTION 



duces a delicate thread which, either directly or indirectly, origin- 

 ates the mycelium upon which the Fungus of the new generation 

 is developed. In the Agarics it is held that a large number 

 of spores germinate, and produce the mycelium from which 

 a single individual or a cluster of young Agarics are evolved. 

 In some instances the mycelium is undoubtedly perennial, and 

 produces a crop of Agarics in successive years, but much remains 

 still to be known of the life -history of the Agarics in the 

 interval between the maturity of the spore and the first 

 evidence of the genesis of a new plant. 1 In some of the smut 

 Fungi the germinating spore produces a thread which develops 

 secondary spores, and these in their turn produce tertiary spores 

 before the true mycelium-forming spores are developed. In the 

 Uredinestihe earliest spore-forms, called "pro-mycelial spores," are 

 produced from the germinating threads of the latest spore-forms 

 or teleutospores, which in turn give rise to the mycelial threads 2 

 that enter and form a new mycelium within the tissues of the 

 invaded host-plant. In the Erysiphei the mycelium forms an 

 external coating on the surface of the living leaves, producing 

 at first conidia, and ultimately the perithecia or spore-capsules 

 of the perfect Fungus. Indeed, as a rule, the mycelium repre- 

 sents the vegetative system of the Fungus upon which, under 

 varied forms, the reproductive organs with their appendages 

 are produced. The universality of this mycelium in Fungi 

 was formerly held to be as certain an indication of distinction 

 between a Fungus and a Lichen as the production of a thallus 

 was then held to be a sufficient distinction between a Lichen 

 and a Fungus. In later times it has come to be understood 

 that the hyphal elements in Lichens and Fungi are virtually the 

 same. 



1 In this connection may be consulted Brefeld's researches into the life-history 

 of Coprirms stereorarius. 



2 See post, chap. xx. 



