PROBLEM I . How S'wrple Anhnals and Vlaiits Reproduce 



417 



Fig. 366 Con'jugatiun in bread mold. The fila- 

 vients from two plants swell at their ends 

 (lower right corner) meet, fuse, ajid form a 

 large zygospore (above), (kune) 



bread mold may reproduce in this way 

 as well as by sporulation. See Figure 366. 



Sexual reproduction. The process you 

 have just been studying is sexual repro- 

 diict'w7i. Two cells, called gametes, fuse 

 or unite with each other. Nucleus unites 

 with nucleus, and cell body with cell 

 body, forming a new cell that is the be- 

 ginning of the new organism. Sexual re- 

 production is the common method of 

 reproduction in animals and plants from 

 the simple to the most complex. 



Contrasted with sexual reproduction is 

 asexual reproduction, in which there is 

 no fusion of cells. Binary fission, bud- 

 ding, and sporulation are all examples of 



Fig. 367 ParaDiecia sometiines co7ipigate and 

 exchange pieces of the sniall nucleus. Then 

 they separate and each divides. How does this 

 differ from co7ijugation in Spirogyra? (kline) 



asexual reproduction. Some species of 

 animals and most plants reproduce sexu- 

 ally at one time and asexually at another 

 time. 



Union of like gametes. When the two 

 uniting gametes are similar in appearance 

 as they are in Spirogyra and in bread 

 mold, the sexual reproduction is called 

 cojijiigatioii. But you will soon see that 

 in most sexual reproduction the gametes 

 are different from each other. When the 

 gametes are different, the process is not 

 called conjugation. It is interesting to 

 note that in the bread mold, although the 

 two gametes seem alike, fusion does not 

 occur unless the threads are of different 

 strains, known simply as plus and minus. 

 Now study conjugation in Parameciu?n 

 (Fig. 367) and if possible do Exercise 7. 



Union of unlike gametes. In the dis- 

 cussion of malaria (see Fig. 311), you 

 read about a union of unlike gametes. In 

 the stomach of the mosquito some of the 

 malarial protozoa become spherical; these 



