976 THE HIGHER BACTERIA, MOLDS AND FUNGI 



Blastospores are thallospores which develop by budding from the end or 

 side of the parent cell and which may in turn throw out another bud or 

 a mycelial filament without becoming detached, and without any period of 

 latency. The buds of yeast cells are familiar examples. 



Arthrospores are thallospores formed by the segmentation of a hypha 

 into a chain of cells at first cubical and later rounded. 



Chlamydospores are single thalospores formed by the concentration of 

 the protoplasm of a hypha into a swollen portion of the filament, the 

 membrane of which becomes thickened. They are purely resting spores and 

 are closely analogous in function to the spores of bacteria. They appear 

 as roughly spherical thick-walled cells much greater in diameter than the 

 hypha3 and are called intercalary if they develop in the course of a continuous 

 filament ; terminal, if at the end of a long hypha or a short lateral branch. 



CLASSIFICATION 



The whole subject of the classification of the fungi is in confu- 

 sion and the phylo genetic relationship of the various groups is 

 obscure. Even the identification of a species is often difficult, partly 

 because some simpler types show little that is distinctive in their 

 structure but chiefly because their morphology varies greatly with 

 changed environment. For example, some of the blastomyces which 

 grow in the animal body as round cells reproducing by means of 

 blastospores, when placed on artificial media develop a mycelium 

 and conidia. Many of the higher forms, too, which are parasitic 

 on plants assume on different hosts forms which bear no resemblance 

 to each other. This pleomorphism has made the study of the fungi 

 a difficult field. A species may be observed for years before it 

 exhibits characteristics which show clearly its relationship to certain 

 other species. 



The modes of spore production are the chief characteristics accord- 

 ing to which the fungi are grouped especially those modes which 

 seem to represent a sexual process. The various species are classed 

 as those which form oospores, or ascospores, etc. Many, however, 

 produce only conidia and it is generally considered that they are 

 degenerate types which have lost the power of even rudimentary 

 sexual reproduction. Such varieties are often grouped together as the 

 fungi imperfecti. As to relationships among these organisms, there 

 is little agreement and almost every writer has brought forward a 

 new grouping and a new classification. There are, however, certain 

 large groups which are generally recognized, the main characteristics 

 of which are shown in the following table : 



