86 FUNGI. 



two main groups of true Fungi : in the Phycomycetes, or Algal 

 Fungi, the mycelium has no transverse walls, and is therefore 

 unicellular, while in the Mesomycetes and Mycomycetes it is pro- 

 vided with dividing walls, which gradually arise during growth, in 

 the youngest hyphse ; intercalary transverse walls may also be 

 formed at a later period. In the hyphaa of some of the Higher 

 Fungi (Hymenomycetes), connections may be formed between two 

 contiguous cells of the same hypha, by a protuberance growing out 

 from an upper cell just above the transverse wall, and forming a 

 junction with the cell below. These are known as clamp-connec- 

 tions- they appear to be of use in affording communication be- 

 tween the two cells. 



The hyphte of Fungi, where they come in contact with one 

 another, often grow together, so that H-formed combinations (fu- 

 sions) are produced, which give rise to very compact felted tissue. 

 When the hyphae are not only closely interwoven, but also united 

 and provided with many transverse walls, the mycelium assumes 

 the appearance of a tissue with isodiametric cells, and is then 

 termed pseudo-parenchyma. The hyphae-walls are sometimes very 

 much thickened, and composed of several layers, and the external 

 layers, by the absorption of water, may often swell very much 

 and become mucilaginous. In some ipstances the walls are colour- 

 less, in others coloured, the most .frequent colour being brown. 

 The cell-contents may also be coloured, and in that case are gene- 

 rally yellow; this colour is chiefly connected with the fat (oil) 

 which may be found in abundance in the Fungi, whilst starch is 

 invariably absent in all the true Fungi. 



The mycelium assumes many different forms ; sometimes it 

 appears as a thread-like, cobwebby, loose tissue, less frequently as 

 firm strands, thin or thick membranes, horn-like plates or tuber- 

 like bodies. The thread-like mycelium may, in the parasitic Fungi, 

 be intercellular or intracellular, according as it only extends into 

 the interstices between the cells or enters into the cells proper. 

 In the first case there are generally found haustoria, or organs of 

 suction (e.g. among the Peronosporacece ; Taphrina, on the contrary, 

 has no haustoria) ; but haustoria are also found among the 

 epiphytic Fungi (e.g. Erysiphacese). Intracellular mycelia are 

 found in the Rust-Fungi, in Claviccps purpurea, Entomophthora, etc. 

 In spite of its delicate structure, this mycelium may live a long 

 time, owing to the circumstance that it continues to grow peri- 

 pherally, while the older parts gradually die off ("fairy rings"). 



