INTRODUCTION 13 



mycelium. The spores of the fungi are of many t3'^pes, but in 

 practically all cases in germination they put out one or more 

 small protuberances which elongate and assume the form of 

 more or less cyHndrical threads. These are termed germ tubes. 

 As they increase in length they tend to branch, and soon a much 

 branched complex of threads constituting the vegetative plant 

 body or thallus is formed. On account of its mould-like aspect 

 in some groups this structure received the name mj^celium. A 

 single thread or branch is termed a hypha (plur. hyphae). In 

 some fungi the development of mycelium is very limited {e.g., 

 Saccharomycetaceae) and in a few groups (Olpidiaccae, Woronin- 

 aceae, Synchytriaceae, Ancylistaceae) the thallus may fail com- 

 pletely to assume the filamentous form. In such cases mycelium 

 is said to be absent. In some of the algae, threads comparable 

 to mycelium are present. In certain bacteria, moreover, the 

 cells remain together in chains forming long threads which are 

 analogous to mycelium. The fungi which lack mycelium resem- 

 ble the other members of the group in the characters of their 

 reproductive processes, and in general are not easily confused 

 with other lower thallophytes. A few (Plasmodiophoraceae, 

 Woroninaceae) approach the Myxomycetes, and correspond with 

 them in that the thallus is a naked protoplast at least in early 

 stages. In the higher fungi a cell wall is always present, and 

 is composed of a modification of cellulose, termed fungus cellulose, 

 which in composition is akin to chitin. In the lower fungi the 

 wall in many forms gives the reaction for true cellulose. Though 

 green plants in general store their food reserve in the form of 

 starch this substance is unknown in the fungi. Instead, the 

 soluble food is transformed into an oil, glycogen, and is stored in 

 the vacuoles. In this connection a consideration of the taxo- 

 nomic position of the genus RhodochT/triumJjSigerheim, containing 

 a single species R. spilanthidis parasitic on ragweed {Ambrosia 

 spp.), is of interest. This organism lacks chlorophyll but stores 

 as starch the food obtained in soluble form from the host. In 

 morphology it corresponds closely with the algal genus Phyllo- 

 hium Klebs (1881). Because it lacks chlorophyll Lindau (1899) 

 places it in the fungi. Other students (Lagerheim 1893 ; Atkinson 

 1908 a, h) incorporate it in the algae. This difference in point of 

 view illustrates the difficulty of drawing a sharp line between 

 the two groups. The green algal genus Chlamydomonas, which 

 in certain classifications embraces some non-chlorophyll con- 



