48 MYCOLOGY 



its extremity, as it grows beneath the bark, or penetrates the soil (Fig. 

 15). Such a compound thallus differs strikingly from the filamentous 

 thalluses of the two previously described fungi. The union of the 

 hyphal cells in some of these fleshy fungi may be so intimate as to con- 

 stitute a pseudoparenchyma, and this close union of the cells may be 

 made still more intimate by clamp connections where two adjoining cells 

 are bound together endwise by a clamp-like protuberance of one of the 

 cells attached to the end of the other adjoining cell. When the pseudo- 

 parenchyma is external, it rnay serve for the protection of the internally 

 disposed hyphae, and be looked upon as protective tissue. Mechanic 

 tissues for the support of fungi are not unknown in some of the groups, 

 as in some of the polypori; where there are clamp connections, trans- 

 verse septa and thickened cell walls. A few of the higher fleshy fungi 

 have conducting hyphae, which are larger and more tubular than the 

 surrounding hyphae, and which conduct later, oil and other substances. 

 Those which conduct a milky juice, as in some species of Russula and 

 Lactarius, may be termed laticiferous hyphs. There are some fungi in 

 which the hyphal form of thallus is not present. The yeasts are either 

 single ellipsoidal cells, or these cells are loosely connected together in 

 a chain of bed-like cells. These chains are due to the budding or 

 sprouting method of cell multiplication where a bud, gemma, or sprout, 

 grows out from the mother cell as a daughter cell. It in turn buds 

 producing a granddaughter cell and so forth. Such a method of 

 reproduction is known as gemmation. 



In the parasitic fungi, the hyphae run either into the cells, through 

 the cells (intracellular), or between the cells (intercellular). Where 

 the hyphae are intercellular, short branches may be formed which 

 penetrate the host cells. These short branches take various forms and 

 are known as haustoria; a single one as an haustorium (Figs. 36 and 67). 

 Occasionally in the mildews, the mycelium may be superficial and 

 hence epiphytic, while the mycelia which are internal are endophytic. 

 These are useful terms when describing the parasitic habits of fungi. 

 Some of the groups of fungi have mycelia that form resting bodies 

 of hyphae. These are the most compact of all forms of mycelia and 

 are known as sclerotes {sclerotium — ia), which in many cases assume 

 tuberous forms. They are resting states of the mycelia and act as 

 stores of reserve material. These are some of the principal forms of 

 the vegetative thallus of the fungi. Further details will be given in 

 he discussion which follows. Some sudden epidemics of rust fungi 



