PART SECOND. 



SYSTP:MATJC AKKANGEMENT OE the CEYrTOGA.AIIC 

 PAEASITES. 



I. THE PATHOGENIC FUNGI OF PLANTS. 



The vegetative body of the Fungi is a thalloid structure 

 known as a mycelium, and composed of one or more hyphae. 

 The hyphae are' cells included in a firm wall of fungus-cellulose 

 of varying composition ; they grow apically, and hence are 

 always filamentous in shape. In the simpler cases, the mycelium 

 is a non-septate tube unbranched or branched ; in the more 

 complex forms, it consists of a system of hyphae divided into 

 cells by cross-septa. By the union and anastomosing of numerous 

 hyphae, a tissue may be formed not unlike the parenchyma of 

 higher plants, hence receiving the name pseudo-parenchyma. 

 Frum this tissue may arise distinct structures of many kinds, 

 such as the sporophores of the Polyporeae, or strands of 

 tissue like tlie well-known rhizomorphs of Ar/aricus mcUeufi, 

 or masses of resting-niycelium like the sclerotia of Claviccps. 

 It is also not uncommon to find a differentiation in the structure 

 of the vegetative mycelium in the form of lateral outgrowths. 

 of the hyphae, developed as organs for the collection of nutri- 

 ment — the haustoria, — or as organs of attachment — appressoria, 

 Ifeproduction may take place sexually by the union of two 

 cells or nuclei, the product of which is a spore or zygote capal^le 

 of germination ; or asexually by means of endogenous spores 

 or swarm-spores, or by the abjunction of conidia of different 

 kinds. Sexual reproduction is common amongst the lower 

 fungi, but in the higher forms, if existent at all, it is very 



