ZYGOTES OF MUCOR 163 



each side. The zygotes are 70 to 80 p in diameter 

 and just visible to the naked eye. Inside the dark, 

 rough outer wall are two layers of inner wall. 



The zygote, in the protoplasm of which a consider- 

 able amount of organic food material, largely fats, is 

 accumulated, is capable of remaining quiescent for a 

 considerable time, the thick outer wall resisting desic- 

 cation. In a suitable medium it germinates, the 

 thick outer wall bursting and the thin inner wall being 

 pushed out by the protoplasm and growing into a 

 new mycelium which often forms a single sporangium 

 at once (Fig. 16, i). 



The zygote of Mucor is a resting stage in the life 

 history, preserving the plant through conditions 

 unfavourable to active growth in the same way as 

 the spores of yeast and bacteria ; while the spores of 

 Mucor, though also a resting stage in the sense that 

 growth of their protoplasm is temporarily suspended, 

 are primarily a means of multiplying and dispersing 

 the individuals of the species, being formed in im- 

 mense 'numbers and much less resistant than the 

 spores of bacteria. 



The process of conjugation, with the formation of a 

 zygote, or product of conjugation, in Mucor is the 

 first example of this process we have met with. As 

 we shall see in later chapters, this process is almost 

 universal in the organic world, though in some of the 

 lower forms it is apparently absent. In Mucor the 

 two conjugating masses of protoplasm are often 

 exactly alike, though in some cases one hypha is 

 larger than the other. The conjugation of two equal 

 protoplasts is called isogamy. 1 



In some kinds of Mucor hyphse from the same 

 1 Greek taog, equal, and yet/tea), marry. 



