140 



of which the green plants make their 

 foods are returned to soil and air for 

 recurrent use in the never ending cycle. 

 Numbered among the more famil- 

 iar kinds of fungi are yeasts, moulds, 

 mildews, blights, rusts, and mushrooms, 



THE BREAD MOULDS 



Tlie investigations conducted by 

 Miss Satina and myself were made 

 upon that group of the fungi com- 

 monly called Bread Moulds and known 

 in science as Mucors. The structure of 

 the plants of this group is simple. Each 

 consists of a branching, thread-like 

 growth devoid of separate cells. In 

 many species of mould the threads 

 grow to a length of from two to four 

 inches, in some, however, they attain 

 a length of from fifteen to eighteen 

 inches. 



At the free end of the thread-like 

 filaments, spherical swellings form, 

 about the size of a pin head. These 

 contain enormous numbers of minute, 

 non-sexual, reproductive bodies called 

 spores. At room temperature, when the 

 air is sufficiently moist, a spore germi- 

 nates readily and grows rapidly on any 

 substance which contains proper nu- 

 trition. Soon a thread-like mass de- 

 velops which, in turn, produces a crop 

 of spore cases. 



As the cycle from spore to spore 

 requires but from one to five days and 

 as each spore case contains a multitude 

 of spores, the spread of the plant, under 

 favorable conditions, may be extraor- 

 dinarily rapid. Indeed, calculations 

 have shown that in some species one 

 spore case may contain 70,000 spores 

 and that each culture which develops 

 as it does from a single spore may form 

 hundreds of spore cases. 



FORMATION OF SEXUAL SPORES 



Although the Mucors are all able to 

 multiply rapidly, perhaps indefinitely, 



LOWER PLANTS, DISEASES, AND MEDICINE 



by means of non-sexual spores, the 

 great majority of these moulds also pro- 

 duce sexual spores, an outcome made 

 possible only when plants of the oppo- 

 site sexes are brought together. Tlie 

 process of the formation of sexual 

 spores (zygospores) can be described 

 as follows: two filaments from plants 

 of the two opposite sexes, provisionally 

 designated as plus and minus sexes, 

 grow toward each other and their ends 

 touch. After contact, food materials 

 flow into these ends producing swell- 

 ings. Cross-walls are now laid down 

 cutring off the two ends so that the 

 young zygospores, at this stage have at 

 least three walls across them. Then the 

 intervening double wall breaks down 

 thereby bringing the contents of the 

 two sex cells into contact. The fusion 

 cell thus formed develops into a ma- 

 ture, thick-walled zygospore around 

 which forms a brown, protective coat 

 with irregular markings. 



IDENTIFYING SEX OF MOULDS 



Male and female plants of the 

 Bread Moulds cannot be distinguished 

 by their appearance or structure, 

 neither does the structure nor function 

 of their sexual cells appear to differ so 

 far as the formation of the sexual 

 spore is concerned. It is therefore not 

 possible to tell by inspection which of 

 the mould plants is male and which is 

 female. 



A very effective method is employed 

 for identifying the sex of unknown 

 races and species. Two Bread Moulds, 

 originally designated as plus and minus 

 strains forty-one years ago, are used as 

 testers. 



For example, if a culture of an un- 

 known race forms zvgospores ^^'hen it 

 is brought into contact with the plus 

 tester, then it is clear that it is a mould 

 of the opposite or minus sex. If, on the 

 other hand, sexual spores develop only 

 in the presence of the minus tester. 



