274 THE AMERICAN MONTHLY [Aug. 



20. Branching Alg^. — Mount and examine pieces of 

 a branching alga in water, study it to distinguish the 

 cells, then study them in turn and attempt to decide by 

 what steps of cell division the aggregate has been built 

 up. Do all cells branch ? Do branches arise at any par- 

 ticular part of the branching cells ? Does more than one 

 branch arise from the same cell ? Are all the cells alike, 

 or can you find cells that are forming spores ? If so, where 

 are they located 'i Can you find any of the spores in the 

 act of developing ? How does a spore differ from an 

 ordinary cell ? 



21. Nutrition in the Chlorophyllogenous Plants. — 

 All of the plants just mentioned can and generally do 

 grow in clear rain water. There is no evidence that any 

 of them require organic food to sustain their life. 

 Though they are constantly building up protoplasm and 

 growing they do not get this from ready-made supplies 

 but form it from carbon-dioxyd, ammonia and water, 

 which abound where they live. They require sunlight 

 and chlorophyll, lo enable them to carry on their chem- 

 ical operations. How does this compare with nutrition in 

 animals as shown by the Protozoa ? Eead on the func- 

 tion of chlorophyll. 



PART IV. NON-CHLOROrHYLLOGENOUS PLANTS. 



22. Yeast. — Mount a small particle taken from a cake 

 of " compressed yeast," add water and thin it consider- 

 ably, and examine uncovered. You will find a multitude 

 of exceedingly minute oval objects and fewer larger oval 

 ones. Add a drop of iodine and examine, you will now 

 be able to recognize the large ovals as grains of starch, 

 the small ones by their brown stain as yeast cells. 



Mount a drop of yeast from a vessel containing 

 Pasteur's solution, in which yeast has been actively grow- 

 ing, thin with water and cover, examine, h. p., and find 



