BUDDING AND SPORE FORMATION 13! 



osmotic pressure within the cell, cytoplasm passing 

 into the bud. The bud grows until it reaches the size 

 of the mother cell, the nucleus of which meanwhile 

 divides, one of the daughter nuclei passing into the 

 new cell. The daughter cell may then be cut off and 

 become a new unicellular yeast plant. So actively, 

 however, does budding take place in a solution contain- 

 ing sugar (with the other necessary elements present 

 in a suitable form) that the daughter cell produces 

 another bud before separation has taken place, and 

 this again another, and thus the chains of yeast cells 

 are formed. A cell may even bud in two or three 

 places at once, so that the chains are branched. 



Spore Formation. Another method of reproduction 

 may occur, however, if the yeast is starved, e.g. by being 

 left on a slab of plaster of Paris with a little water. 

 Under these circumstances the nucleus divides into 

 two and then into four, the cytoplasm withdraws from 

 the wall and becomes aggregated round the four neclei 

 in four tiny spherical masses, each of which secretes a 

 comparatively thick wall (Fig. 14, D). Each of the 

 spores so formed is about 3 \i in diameter. If now the 

 yeast culture dries up, the original cell wall collapses, 

 and the spores can be carried away and float with 

 the dust in the air, the living contents remaining in 

 a dormant condition for a long time. Falling into a 

 suitable liquid medium, the dormant protoplasm of 

 the spore absorbs the liquid and becomes active, burst- 

 ing the spore wall, pushing out, and covering itself 

 with a new ordinary cell wall, thus giving rise to a new 

 vegetative yeast cell. 



The spores of yeast are therefore a resting stage in the 

 life history, able to withstand desiccation for some time. 

 This is true of most of the spores formed by plants. 



