194 THE HIGHER FUNGI : CARPOMYCETEAE 



reach them (e.g., Sclerotinia sclerotiorum (Lib.) de By.) to extreme cases 

 of balanced parasitism (e.g., some of the Ustilaginales in which the 

 fungus and host, together grow for a long time with little apparent harm 

 to the latter). One large group has developed a special type of parasitism 

 upon terrestrial or epiphytic fresh-water algae, forming peculiar struc- 

 tures which enclose the algal hosts. These are the Lichens. Some of the 

 most harmful fungi from the economic standpoint, the Rusts and Smuts, 

 are found among the Higher Fungi. 



Reproduction 



Asexual reproduction by means of conidia is widely distributed 

 throughout the various classes and orders, but seems to be entirely lack- 

 ing in some of the groups. The conidial production may consist of the 

 abstriction of a single cell from the tip of a short, unbranched conidiophore 

 or the conidiophore may be longer and branched. The conidia may be 

 produced successively at the tip, separating from the conidiophore as 

 soon as formed or clinging together in a mucilaginous drop or remaining 

 attached in a chain. A chain of conidia may produce new conidia acro- 

 genously, i.e., each new conidium arises from the apical conidium of the 

 chain, so that the basal conidium is oldest and the apical one the last 

 formed. This is the type of conidial formation in Cladospoi'ium, Alteniaria, 

 etc. On the other hand the conidial formation may be basigenous, i.e., 

 each new conidium is produced at the apex of the conidiophore just 

 below the last formed conidium (e.g., Erysiphaceae, Aspergillaceae). A 

 third method of formation of chains of conidia is the almost simultaneous 

 rounding up of the cells of a simple or branched hypha into catenulate 

 conidia. These conidia then fall apart almost simultaneously (e.g., Moni- 

 litiia, Oospora, etc.). Where the conidia formed in this manner are small 

 they are often called "oidia." 



The conidiophores may be scattered or crowded or enclosed in a 

 hollow structure provided with an apical opening (i.e., produced in a 

 pycnidium). If the conidiophores become laterally crowded and adherent 

 into a column we have a coremium, such as is formed in species of Peni- 

 cillium under certain environmental conditions. 



The conidia themselves may vary greatly in size and shape as well 

 as color and number and arrangement of cells. In general we may dis- 

 tinguish conidia destined for distribution by air currents and those that 

 are distributed by other means. The latter are usually surrounded by a 

 sticky substance when wet and cling to anything with which they come 

 in contact, drying down and becoming firmly attached when dry. When 

 wet by rain such conidia may be scattered by the currents of water 

 running on the surface of the substratum or may be splashed about by 

 the falling rain drops and distributed by the wind which carries these 



