CELLULAR STRUCTURE OF ORGANISMS 101 



Oarchesium. Colonial forms of Vorticella-\ike organisms, either Car- 

 chesium or Zoothamnium, ma^y usually be found in aquaria in which various 

 fresh-water plants are kept. The dishes which have been prepared for the 

 culture of Amoeba and Paramedum will frequently show them. If they are 

 obtainable they should be studied. No special methods are necessary, the 

 colonies being small enough to be placed under a cover glass and studied 

 alive. Staining with methylene green is useful to bring out the nuclei. 



Ulothrix or Spirogyra. One of these forms should be studied as an 

 example of filamentous plants. Either of them may be found in 

 ponds or ditches by the roadside. They are to be studied without any 

 special preparation, the fresh form showing most points perfectly well. 

 The shape of the cells and of the chlorophyll bodies should be noticed. 

 The nucleus may usually, though not always, be seen without any treat- 

 ment. A little glycerine added underneath the cover glass will cause the 

 protoplasm to contract from the cell walls. Staining with methylene green 

 will show the nucleus if it has not been seen without this. If material is 

 at hand to show the conjugation, it is desirable to have the student study 

 threads of conjugating Spirogyra and compare with the conjugation of 

 Paramedum described in the text. The reproduction of Ulothrix by for- 

 mation of spores is so difficult to obtain that it is impractical to furnish 

 material to a class for study. 



Penicillium and Other Molds. Molds may be easily obtained by allowing 

 bits of lemon, banana, bread, etc., to remain for a few days in a closed jar 

 in a warm place. The general appearance of the molds can be studied on 

 the surface of these articles. For a more careful study it is necessary to 

 study the colonies growing from spores. A simple method is as follows: 

 Prepare a culture medium from dried beans by placing a pint in about twice 

 as much water as is necessary to cover them. Allow to stand 12 hours and 

 add enough water just to cover the beans. Then strain off the liquid from 

 the beans and filter. To the filtrate add 1% of agar and boil so as to 

 completely dissolve the agar. Place the material in test tubes, about 10 

 c. c. in each, and plug the mouths of the tubes with cotton. Place in a wire 

 basket and sterilize by steaming for three-quarters of an hour on three 

 successive days. To use this culture medium, melt several of the tubes 

 of agar and pour each into a petri dish, allowing the agar to harden. When 

 thoroughly hard, remove with a platinum needle a minute quantity of 

 the spores, which appear on the mold on the lemon or bread, and just touch 

 the surface of the agar with the spore-laden needle tip in several places. 

 This will sow the spores. Place the petri dish (covered to prevent drying) 

 in a warm place. This dish may then be studied from day to day by 

 putting it under a microscope, and the sprouting of the spores, the 



