1 6 INTRODUCTION TO THE STUDY OF FUNGI 



We have biietly directed attention to the ordinary develop- 

 ments of mycelium, whether filamentous or sclerotioid, but 

 there are still one or two special modifications which must 

 obtain a passing reference. Of these the mycelium of the 

 Uredineae is deserving of mention, being formed within the 

 tissues of living plants, and often starting centrifugally from a 

 definite point of infection. The hyphae resemble ordinary 

 mycelial filaments, but, like all internal mycelia, are delicate, 

 branching and anastomosing so as to form compact cushions or 

 spore beds, or, in other cases, much diffused and scattered. In 

 annuals or upon deciduous parts the mycelium is, of course, only 

 annual, but if it passes into perennial parts, as it may readily 

 do in shrubs and other perennials, the mycelium becomes 

 perennial. Take, for instance, the Juniper, in which the 

 Crymnosporangium may be sought for and expected regularly 

 year after year. In such species as have a scattered mycelium 

 there is not much difference between the mycelium of these 

 and that of other endophytes, but when the mycelium is 

 circumscribed, the tissues are hypertroj)hied, and starch seems 

 to be accumulated in the deranged cells. Leaves thus attacked 

 never repair the injury, and the diseased spots are the first to 

 die, and occasionally drop out, as we have seen with the large 

 clusters of perfect-spored pustules in Puccinia deanthi. The 

 mycelium of the Feronosporeae is more diffused than that of 

 the Uredines, commonly penetrating the whole plant, descend- 

 ing into the stem and roots, and in the stems producing oospores, 

 as the result of a sexual conjugation. In the Ustilagineae the 

 mycelium is much more diffused than is usual in the Uredines, 

 permeating the entire plant, and in perennial hosts producing 

 fruit regularly year after year. 



The Phycomycetcs, which include those mould-like Fungi 

 which bear inflated sacs at the apices of their fertile branches 

 containing numerous spores (Ilucors), have a mycelium without 

 septae. The Mucors themselves are mostly saprophytes, and 

 some of them have a profuse mycelium. The reproduction is 

 both asexual and sexual, the sexual being developed from the 

 mycelium ; hence the mycelium in these Fungi, although at first 

 only vegetative, becomes finally reproductive, and thus assumes 

 a higher function. The process is after this kind : two short 



