ANATOMY OP^ FUNGI 45 



margin of the hymenium and edge of the sporophore : thus 

 the hymenium of each succeeding year occupies a greater 

 area than the previous one it is built upon. Owing to this 

 successive formation of one hymenium upon another, 

 a section of the fungus shows a stratified appearance, and 

 the age of the fungus can be determined by counting the 

 number of superposed layers of tubes, assuming that 

 a layer had been formed each year, which takes place 

 under normal conditions. In like manner the addition 

 each year to the margin often forms a corresponding 

 ridge on the sterile upper surface of the pileus, and the 

 succession of ridges and differently coloured zones on the 

 surface of the pileus of perennial species are explained in 

 this manner. 



The spores or reproductive bodies in the broader sense, 

 including conidia, present a very varied sequence of general 

 form and structure. In all the Basidiomycetes the spores 

 are one-celled or continuous ; this is also true of large 

 numbers of conidia. In the Protobasidiomycetes the 

 spores often consist of more than one cell, or, as expressed 

 by systematists, the spore is one-septate, or consisting of 

 two cells ; when three-septate the spore consists of four 

 cells. The reason for this is, all spores are at first one- 

 celled ; then, if the spore is of an elongated form, a trans- 

 verse wall or septum first appears dividing the cell into two 

 equal portions, or cells ; each cell then undergoes division 

 in a similar manner, the result being a three-septate spore, 

 or a four-celled spore, whichever term is favoured by the 

 systematist. By the continued formation of transverse 

 walls a multiseptate or multicellular spore or conidium is 

 formed. In many instances, more especially in the case of 

 spores produced in asci, septa are formed at right angles to 



