56 - The Cell 



Fig. 3-12. Parent Hydra, with two buds. (Copyright, 

 General Biological Supply House, Inc.) 



parts, each part then grows into a new indi- 

 vidual. And even such highly organized 

 creatures as earthworms can behave in simi- 

 lar fashion, if cut into two pieces of fairly 

 equal si/e. 



Budding. Budding is similar to binary fis- 

 sion except that the two pans into which the 

 body divides are conspicuously unequal. A 

 most familiar example of budding is found in 

 dividing yeast cells (Fig. 10-0). Here it is seen 

 that one of the daughter cells receives only 

 a minor share of the cytoplasm, although the 

 nucleus of the smaller is eqtial to that of the 

 larger daughter cell. The smaller daughter 

 cell, called the bud, thus retains a full po- 

 tential for growth and activity. In time the 

 bud may catch up with its larger sister, 

 which meanwhile may continue to give off 

 other buds. In an undisturbed medium the 

 yeast cells may cling together for several 

 generations and thus give the appearance of 

 a small branching filament. However, their 

 attachments are tenuous, and permanent 

 colonies are not formed in this particular 

 kind of plant. 



Budding is fairly common among proto- 



zoans, and it occurs also in some multicellu- 

 lar plants and animals. In the latter case, 

 however, the bud is not a single cell, but an 

 aggregate of cells derived by mitosis from the 

 cells of the parent. In Hydra, for example, 

 the bud develops into a small but complete 

 new individual before it becomes detached 

 and independent (Fig. 3-12). 



Sporulation. The formation of reproductive 

 spores is very common among simpler organ- 

 isms, and practically universal among higher 

 plants. Typically each spore-forming cell 

 undergoes two or more divisions in rapid suc- 

 cession, producing four or more spores. Fre- 

 quently the sporulation divisions are meiotic, 

 so that usually the spores are haploid. The 

 spore, unlike an egg or sperm, develops into 

 a new individual without any process of fer- 

 tilization. The sporulation divisions often 

 occur inside the cell wall of the spore mother 

 cell (Fig. 3-13); and usually each spore de- 

 velops its (n\n tough casing, making it re- 

 sistant lo dry conditions. Certain veasts re- 

 produce not onlv by budding but also by 

 sporulation. When the medium in which the 

 leasts live begins to dry up, or becomes other- 

 wise unsuitable lor life, each of the cells 

 divides into four equal spores, possessing in- 

 dividual protective covers, but all contained 

 within the original cell wall (Fig. 3-13). Later 

 this outer casing ruptures and the liberated 

 spores may be blown about in the dry atmos- 

 phere without suffering death from loss of 

 water. Finally the spore may chance upon a 



Fig. 3-13. Spore formation in yeast cells (unstained). 



