ORDER SACCHAROMYCETALES 335 



from branched ascogenous hyphae. Furthermore there is lacking the 

 formation of a protective structure, the perithecium or apothecium. 



The mycelial forms of this order mostly take on the unicellular (i.e., 

 yeast) habit when growing in nutritive media of considerable concentra- 

 tion. On the other hand many of the yeasts can be made to develop more 

 or less typical hyphae when grown on special media, usually those not too 

 rich in soluble organic substances. In the main the species that have the 

 yeast habit possess uninuclear cells. That is also true of many of the 

 filamentous forms, although some of the latter may have several nuclei to 

 the cell. 



The majority of Saccharomycetales are saprophytes on organic mat- 

 ter, mostly of vegetable origin. However, some are parasites in plants 

 (e.g., species of Nematospora) or in Man or other animals. When growing 

 as saprophytes in organic media of plant origin they frequently cause fer- 

 mentation, the products usually being CO2 and various alcohols or organic 

 acids. Some species of Saccharomyces are of very great importance, espe- 

 cially in the commercial production of alcohol for industrial or beverage 

 purposes, or of CO2 for leavening bread. Many of these fungi can grow 

 anaerobically if sufficient soluble organic foods are present in the medium. 



As in most of the Ascomyceteae in which such studies have been made 

 the cell walls are mostly lacking in cellulose but it is not agreed whether 

 or not chitin is present. In Schizosaccharomyces octosporus Beij. and Sch. 

 vcrsatilis Wick. & Duprat (1945) the ascus walls give a distinct blue reac- 

 tion with iodine-containing media, indicating the presence of carbo- 

 hydrates closely related to dextrin or starch. This should be compared 

 with the similar staining of the apical portions of the asci of some Pezi- 

 zales and of the b^-sidiospore walls of some Agaricales. 



In the filamentous forms asexual reproduction may take place by ter- 

 minal or lateral budding from the hyphal cells or by the breaking up of 

 the hyphae into short unicellular pieces, often called "oidia." Short 

 conidiophores may be produced in some species which bear conidia singly 

 or in short chains. The unicellular forms may reproduce by fission into 

 equal cells which remain adherent at first and eventually separate from 

 one another. These are the Fission Yeasts. The majority of the yeasts 

 however reproduce by the formation of small buds which enlarge until 

 they equal the mother cell in size. In the meantime other buds may arise 

 on the mother cell and on the buds already in process of development so 

 that a colony results consisting of many cells of various sizes and ages. In 

 the process of budding a small bud is produced and then into it projects 

 an extension of the nucleus of the mother cell. According to Lindegren 

 (1945, 1949) this extension separates by mitosis from the mother nucleus 

 and then the opening between the two cells is closed except for a small 

 central pore which always remains through the separating septum in all 



