Fig. I. Asexual reproduc- 

 tion. ( I ) Fission as it occurs 

 in amoebae and bacteria. 

 (2) Budding in yeast. (3) 

 Filamentous growth in 

 molds. (4) Fragmentation 

 in Plasmodium malariae. (5) 

 Nonceilular growth in the 

 myxomycetes. 



Plastic cells ^;;^ 



Rigid < 



2 Budding 



3 Filamentous growth 



4 Frogmentotlon 



5 Non-cellulor growth 



rapidly to the approximate size of the mother and finally constricts off. It 

 may separate completely from the mother or may remain attached. In the 

 latter case, both mother and daughter may bud and so produce a chain 

 of cells. This is the manner in which yeast cells divide. 



3. Growth of filaments. The cells of fungi and some algae are linked 

 together in thin hair-like fibers. Since growth can occur only at the tip 

 of each filament, the tip elongates and a cross wall forms to yield a cell 

 with a growing tip on its far end. Branching often occurs, when the 

 growing tip bifurcates and both branches elongate in separate strands. 



4. Fragmentation. The animal parasite, Plasmodium malariae, is one 

 of a number of microorganisms that reproduce by fragmentation. The 

 Plasmodium grows inside a red blood cell. The parent nucleus divides or 

 fragments into as many as 24 daughter nuclei and the cytoplasm coalesces 

 about each of them. Separate walls are formed around the conglomerates 

 of nucleus and cytoplasm, which are now called merozoites. The host red 

 cell ruptures and releases the merozoites and each can now infect another 

 red blood cell. (Incidentally, the well-known chills and fever of malaria 

 are associated with the simultaneous release of merozoites from many 

 blood cells.) The term fragmentation is a bit misleading because the 

 parent organism does not break up into incomplete fragments, each of 

 which reconstitutes a whole new organism. Rather it is as if a bacterium 

 would synthesize enough protoplasm to create many new cells instead 

 of just two. Many kinds of molds, algae, and protozoa form large numbers 

 of spores ^ at certain stages of their life cycles. In principle, the process 

 resembles that of Plasmodium malariae. 



5. Nonceilular growth. A few simpler organisms can grow exten- 

 sively without cell division. A group called the mycetozoa consists of 



1 Special cells with thick walls that resist drying, heat, and radiation and which 

 can lie dormant for long periods of time until permitted to germinate. 



7 



