GENERAL MORPHOLOGY OF FUNGI 19 



still recognizable as such, they are referred to as prosench3rma ; if the hyphae 

 have lost their individuality so that they lie adjacent, with the cells (in sec- 

 tions of the tissue) appearing isodiametric and continuous, they are called 

 pseudoparenchyma since they are formed by cell division in a single plane 

 while the parenchyma of higher plants develops from cell division in three 

 planes. 



Sclerotia are small hard masses of plectenchyma with a firmer pseudo- 

 parenchjrmatic rind and a looser prosenchymatic core. These structures serve 

 to carry the organism over unfavorable environmental conditions and, with 

 the return of normal conditions, germinate to the usual mycelium or to a 

 fructification. Sclerotia are formed on drying out of the culture in many 

 species of Aspergillus. Bulbils are small sclerotia formed of a few layers of 

 cells and are often present in large numbers. The grains in the lesions of 

 mycetomas (Madura foot, etc.) belong in this general category. 



Reproductive Structures. — In most fungi, at a definite age and imder 

 favorable conditions of nutrition, reproductive structures develop on the 

 mycelium. The products of the reproductive processes are chiefly spores. 

 Spores may be defined as characteristically formed cells or groups of cells 

 which separate from the mother plant and may grow independently to new 

 individuals. They serve either for propagation (multiplication and dispersal) 

 or for resisting unfavorable conditions of the environment (prolonged desic- 

 cation, overwintering, etc.). Spores specialized for the latter function are 

 often called hypnospores (Fig. 1). 



In the simplest case, hyphal cells separate from the parent hyphae and 

 develop into new hyphae. These individual cells are called arthrospores or 

 thallospores and are homologous with the cells of a chain of blastospores, 

 though the latter arise by sprouting rather than by the breaking apart of the 

 cells of a hypha (Fig. 2). 



From arthrospores there is a gradual transition to more typical spores 

 with characteristic color, form, and sculpturing of the wall. In many cases 

 they are abjointed directly from the cells of an ordinaiy hypha ; in other cases 

 they arise on specialized sporophores. AVhere these sporophores form the 

 spores within specialized sporogenous cells, sporangia., they are called spor- 

 angiophores and the spores, if they are enclosed and nonmotile, sporangia- 

 spores (e.g., in the Mucorales). Sporophores which abjoint their spores ex- 

 ogenously at their tips are referred to as conidiophores and their spores 

 conidia (e.g., in the Fungi Imperfecti). A chlamydo spore is any thick-walled 

 asexual spore without further regard to its morphologic significance. 



In the higher fungi, the mycelium surrounding a group of conidiophores 

 (or sexual organs) is known as a fructification. When these groups are in 

 fascicles, they are called coremia (Fig. 3) ; if they form widespread cushions, 

 they are called sporodochia (Tuberculariaceae) or acervuli. The tissue from 

 which they arise is then known as their stroma. When the conidiophores 

 develop in cavities in the stroma, the finictifications are called pycnia, and 

 the conidia are often called pycnospores or stylospores. These different spore 



