A MANUAL OF BOTANY 115 



of the reproductive structures, plates, sperms, and an en- 

 larged oogonium, all (Ip). 



Marl. Many small lakes supjjort a vast growth of this 

 plant, and it in reality produces from the chemical elements 

 found in the water a carbonate of lime preparation mixed 

 with other elements that foi-m marl. Ascertain the value 

 and use of marl in the manufacture of Portland cement. 



SECTION 11. THE FLNGP 

 Type 1. Yeast ^ 



Yeast preparations. Examine different forms of yeast 

 preparations furnished by the instructor, as yeast cakes, 

 compressed yeast, and liquid yeast. Observe in each the 

 peculiar odor. Where is yeast obtained ? Find out some- 

 thing, if you can, about its preparation on a large scale for 

 the market. Ask your grocer how long he can keep the 

 different kinds of yeasts. Find out how some of your 

 bread-making friends make yeast, and decide, after careful 

 comparison with the following study, if, after all, it is 

 really made, or is something that is grown or prepared. 



Home experiments. jNlix for yourself, at home, yeast of 

 some sort with water, a little flour, and a small amount of 

 sweetening, and place where the mixture will remain warm. 

 Examine frequently the results. 



Note. If possible, put the mixture in a deep, wide-moutliod bottle 

 that can be corked. When freshly mixed, light a taper and insert in 

 the bottle for a moment only. After the yeast begins to foam or 

 bnbble freely, cork for some hours ; then remove the cork and quickly 

 insert the taper lighted. Compare with the results of the first trial. 

 What gas is being made by the yeast ':* Compare by breathing into a 

 deep, clean bottle, and then trying the lighted taper for results. 



Microscopic structure. Examine some prepared yeast mix- 

 ture with (Ip), and particularly with (hp), and observe the 



1 Thallus plants without chlorophyll. - An imperfect fungus. 



