142 



LOWER PLANTS, DISEASES, AND MEDICINE 



then the race in question belongs to the 

 other or plus sex. 



It is also possible, in a similar way, 

 to identify the sex of species other than 

 that to which the two plus and minus 

 testers belong. 



A race, the sex of which is to be de- 

 termined, is brought into contact with 

 the plus and minus testers, as before. 

 If it belongs to the plus sex the begin- 

 nings of sexual reactions will be ob- 

 served at the point where the unde- 

 termined race come into contact with 

 those of the minus tester. 



Tlireads of opposite sex meet and 

 produce swellings which enlarge and 

 sometimes form sexual cells, but the 

 sexual cells never fuse as they do when 

 the opposite sexes belong to the same 

 species and consequently no fully ma- 

 tured sexual spores will be formed. The 

 sexual reaction, although begun, is not 

 carried to completion. 



BIOCHEMICAL TESTS FOR SEX 



Although it is impossible to distin- 

 guish the plus and minus moulds from 

 appearance, a distinct difference be- 

 tween opposite sexes can be shown 

 when they are subjected to certain 

 chemical tests. 



If part of the oxygen in a solution 

 of potassium permanganate be re- 

 moved (reduced), the purple color of 

 the solution changes to pink-yellow or 

 it may become decolorized. Various 

 substances added to the purple solution 

 will bring about these changes in color 

 through their effect as a reducing agent 

 of oxygen. Many tests with extracts pre- 

 pared from the thread-like masses of 

 plus and minus races of moulds have 

 shown that in the majority of eases the 

 extracts of the plus races produce a 

 greater change in color of the potas- 

 sium permanganate than the extracts 

 of the minus races. The plus races are 

 also stronger reducers than the minus 

 races. 



In the amount of sugar which can 

 be extracted from the plus and minus 

 races, lies another distinct biochemical 

 difference between the two races. Care- 

 ful tests repeated many times indicate 

 that the plus races contain a higher 

 average sugar content than do the 

 minus races. 



This study of sex in moulds is a 

 fundamental study in establishing a 

 chemical basis for sex differences in 

 what appears to be structurally iden- 

 tical strains of Mucors. 



QUESTIONS 



1. Mention the two main reproductive 3. Is there any way by means of which 

 methods by which bread molds rcpro- the plus and minus strains can be told 

 duce. apart? 



2. Describe sexual reproduction in bread 

 molds. 



