FLOWERLESS PLANTS 167 



for tiny clear areas in the cells; these are vacuoles, or spaces filled with 

 fluid. The nucleus is hard to find in an unstained yeast cell; it can, how- 

 ever, be found in specimens which have been prepared by staining the .pre- 

 viously killed cells with iron-haematoxylin. (See Lee, Vade Mecum or 

 Sedgwick and Wilson, General Biology.) Yeast cells grow rapidly and re- 

 produce by a process of budding. Look for cells with smaller cells attached. 

 Is there ever more than one cell budded off from a parent ? 



Draw several cells, showing buds as they appear to you under the high 

 power of the compound microscope. 



Spore Formation. — Most yeast plants seem to produce spores at some 

 time during their existence. The spores are formed within a yeast cell, 

 as many as four being produced within a single cell. These spores, under 

 proper conditions, will germinate and form new plants. The yeast forms 

 ascospores. 



Conditions Favorable to Growth of Yeast. — Under certain conditions 

 yeast, when added to dough, will cause it to rise. We also know that yeast 

 has something to do with the process we call fermentation. The following 

 experiments will throw some light on these points: — 



Label three pint fruit jars A, B, and C. Add one fourth of a compressed 

 yeast cake to two cups of water containing two tablespoonfuls of molasses 

 or sugar. Stir well and divide into three equal parts. Place one portion 

 in each jar. Put one jar in the ice box on the ice, and one over the 

 kitchen stove or near a radiator; boil the third jar by immersing it in a 

 dish of boiling water, and place it next to B. Lay the covers on the 

 jars. After twenty-four hours, look to see if any bubbles have made their 

 appearance in any of the jars. Notice the color, taste, and odor of each jar. 

 Lower a lighted match in a jar in which bubbles are rising. What gas is 

 formed by the growth of yeast ? 



This experiment shows that yeast plants, like most other forms of plant 

 life, will not grow in a cold atmosphere, and that they may be killed by 

 too much heat. They grow freely in solutions containing sugar. Experi- 

 ments may be performed to test whether they will grow in distilled water 

 (which contains no organic matter), and as to their growth in pond water. 

 They thrive in a solution containing compounds of nitrogen, named after its 

 discoverer, Pasteur's solution.^ Yeasts are saprophytes. In order to grow, 

 they must be supplied with food materials that will build up protoplasm 

 as M^ell as release energy. 



Fermentation A Chemical Process. — In this process of growth the sugar 

 of the solution in which they live is broken up by a digestive ferment or 



^ The formula is : — 



838 c.c. distilled water. 



10 c.c. ....... ammonium tartrate. 



150 c.c. saturated solution of grape sugar. 



2 grams magnesium sulphate. 



2 grams calcium phosphate. 



2 grams potassium phosphate. 



