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TEXTBOOK OF BOTANY 



These two projections (which are themselves really short branches) 

 grow in length, their ends being in contact all the time (Fig. 24, A, B); 

 they look much like the projections which form the conjugation tube 

 of Spirogyra. Next, the end of each projection becomes a separate 

 ceU cut off by a wall from the rest of the projection (Fig. 24, C). The 

 two short end cells thus formed are the gametes. The walls of the 

 two gametes are now dissolved where they touch each other, and the 

 gametes unite to form a single cell — the zygote. The zygote becomes 

 a large, spherical cell with a thick wall, stiU attached by short branches 

 to both the parent plants (Fig. 24, D). Of 

 the branches which bear the gametes, one is 

 somewhat smaller than the other, and the 

 smaller branch usually bears a smaller 

 gamete than the larger one. 



85. Germination of the Zygote (Fig. 25). 

 — The zygote of Rhizopus, like that of 

 Spirogyra, is a resting cell; that, is, it may 

 remain for a long time without apparent 

 change and still be able to germinate when 

 conditions become favorable for the growth 

 of the plant. When the zygote germinates, 

 a swelling appears on one side, much as in 

 the germination of a spore ; this swelling 

 grows, not into a large, much-branched plant 

 like the one we have studied, but into a short 

 stalk, which, like the upright branches of the 

 ordinary mold plant, bears a spore sac. The 

 spores produced in this spore sac germinate 

 in turn into branched plants exactly like the 

 plant that we studied first. Thus, instead 

 of developing a single ordinary plant from each zygote, as Spirogyra 

 does, the mold forms many spores almost at once, and so a great many 

 mold plants result from the germination of a single zygote. 



86. Advantages of Spore Formation. It is plain that this 

 method of quickly multiplying its numbers after a zygote 

 germinates is very useful to the mold, especially as the zygotes 

 are scattered about and subjected to all kinds of unfavorable 

 conditions, and it is probable that only a small proportion of 

 them ever germinate. The same sort of advantage to the 

 plant results from the production of spores throughout its 



Fig. 25. — Germination 

 of a zygote of Rhizopus. 

 After Brefeld. 



