SAPROPHYTES AND PARASITES 683 



more delicate, hyphal filaments or germ-tubes {t, Fig. 229), which, 

 if properly nourished, develop at once into mycelia. 



Where the spore possesses a double wall, the inner or thin 

 cell-membrane forms the germ-tube : the latter often makes its 

 exit through pores or thin places in the outer firm coat of the 

 spore. 



In some conidia, especially when placed in nutrient solutions, 

 the cell-wall bulges out at one or more points, the outgrowths 

 grow larger and larger until they equal the parent cell in size 

 and form. Each daughter-cell behaves in the same manner, 

 and although the various generations of cells may remain for a 

 time connected in the form of chains, they ultimately become free 

 from one another. Such cell-multiplication (Figs. 240 and 253) 

 is termed sprouting or budding; it is frequent in many different 

 orders of fungi, and very characteristic of the true yeasts {Sac- 

 charomyces). 



As previously mentioned, chlamydospores on germination 

 produce a more or less simple and short hypha, termed a 

 promycelium, which does not develop further vegetatively, but 

 often gives rise to spores at once. 



7. Mode of Life : Saprophytes and Parasites. — On account of 

 the absence of chlorophyll and chloroplasts, fungi are unable 

 to manufacture the complex carbon compounds necessary for 

 their nutrition from carbon dioxide and water ; they are there- 

 fore compelled to obtain these compounds ready made from 

 other sources. 



Those species which derive their food from the organic com- 

 pounds of dead plants and animals are spoken of as saprophytes. 

 Although many saprophytes feed upon and induce, what is 

 termed decay and putrefaction in jam, cheese, bread, and other 

 foods, and also cause 'dry -rot' and other injuries to timber, as 

 a class they perform useful work in clearing the surface of the 

 earth of dead bodies of animals and plants which would, other- 

 wise, rapidly accumulate to an objectionable extent. Moreover, 



