LABORATORY AND FIELD WORK 403 



moist filter or blotting paper under a battery jar or in a covered 

 evaporating dish, so that the water on the slide will not evaporate. 

 In such a culture find spores and young plants showing different 

 stages in germination and growth. 



14. Notice that germination begins by a swelling of the spore; 

 next there appears a projection (or sometimes two or three pro- 

 jections) on the surface of the spore. Follow the growth of a 

 projection. Into what does it develop? How long is it before 

 the first branch appears ? 



15. Make outline drawings of three stages in the germination of 

 the spore. 



16. If spores from plus and minus strains of Rhizopus ^ are 

 mixed and sown upon bread, gametes and zygotes will be formed 

 at the places where branches from plants of the two strains come in 

 contact. Or if a culture of Sporodinia (the mushroom mold) can 

 be, obtained, it will be found to produce gametes and zygotes, be- 

 cause in this mold conjugation occurs between gametes formed 

 on different branches of a single plant. 



17. Notice the outgrowth of swellings from two neighboring 

 branches. The swellings grow into short branches whose ends 

 are in contact. Look for the following stages : 



a. Cell division, resulting in the formation of a gamete at the end 



of each short branch. 



b. The disappearance of the walls of the gametes where they touch 



each other. 



c. The union of the gametes into a single cell — the zygote. 



d. The growth and rounding up of the zygote. 



e. The formation of a thick wall about the zygote. Is this wall 



smooth? What is its color? 



18. Are the short branches which bear the gametes alike? 

 Are the gametes themselves alike ? 



19. Compare conjugation in the bread mold and in Spirogyra. 



20. Draw a ripe zygote with the short branches which hold it, 

 showing the attachment of the latter to the longer branches of the 

 parent plant or plants. 



1 Cultures of the separate strains may be obtained from some of the companies 

 that supply plant materials for class use. 



