FUNGI 



the two nuclei (of separate sexual origin) are present in a cell within one 

 nuclear membrane (i.e., a diploid nucleus) or each in its own separate 

 membrane (i.e., two haploid nuclei in the cell), the effect on the cytoplasm 

 is practically the same, so that a dicaryon cell is to all intents and pur- 

 poses a diploid cell. Thus when Buller (1930) speaks of the "diploidiza- 

 tion" of a monocaryon mycelium by the introduction of a compatible 

 haploid nucleus which multiphes and spreads from cell to cell this term 

 is essentially correct although the nuclei, now in pairs in each cell, are 

 still haploid. He was speaking of diploidization of the cell as a whole 

 not of the contained nucleus. 



In the simplest fungi the whole plant, consisting of but one cell, 

 becomes the reproductive unit that produces the asexual or sexual cells. 

 As we study fungi of greater complexity we find that the vegetative and 

 reproductive portions of the organism are more and more segregated. 

 In many fungi the process of sexual reproduction becomes increasingly 

 complex and leads to the formation of, not a single zygote, but a very 

 complex structure, the spore fruit, many of whose cells become the ulti- 

 mate reproductive spores. Some of the puffballs, e.g., Calvatia gigantea 

 (Batsch ex Pers.) Lloyd, attain a diameter of over one meter. This is the 

 spore fruit. The vegetative mycelium is subterranean and not noticed 

 except when hunted for. 



Parasitism. Because of their lack of chlorophyll all fungi must obtain 

 their organic food from sources external to themselves. The whole my- 

 celium may have the power to absorb these foods or this task may be 

 relegated to special portions such as rhizoids or to haustoria, the knob-like 

 or finger-like processes that enter the cells of the host plant. In many of 

 the Phycomyceteae there is a great difference between the much branched 

 mycelium within the substratum and that portion outside which bears 

 the reproductive organs. 



Probably the majority of fungi are saprophytic, i.e., feed upon the 

 organic products or remains of plants or animals but not upon the hving 

 organisms themselves. The substances utilized by the fungus are often 

 very varied in nature. Simple sugars, starches, cellulose, or organic acids 

 may satisfy its needs provided the necessary mineral nutrients are present. 

 On the other hand some fungi require the presence of various growth 

 factors, such as biotin and thiamin, and some proteins or their building 

 blocks, the amino acids. Some saprophytic fungi are much more limited 

 as to their organic foodstuffs. In general, however, their range of foods 

 is far wider than that of strict parasites. Some facultative parasites are 

 able to grow apparently indefinitely as saprophytes. Thus a species of 

 Fusarium capable of causing the death of Sesamum indicum L. was studied 

 in culture by the author (1904). When provided with the necessary 

 mineral nutrients, it developed upon cellulose, simple and complex sugars. 



