LABORATORY STUDIES 25 



grass leaves or other plants. Mount in dilute potash. 

 Threads will be found showing the formation of new cells 

 (spores) by fission. 



(6) Add a little sugar (preferably glucose) to a little potato 

 water (made by grating up a raw potato and heating with 

 water to extract the soluble matter and filtering) and break up 

 in it part of a yeast cake ("compressed yeast") setting the 

 solution in a warm place. Examine a small drop of the scum 

 or sediment after a few hours for cells showing the type of 

 fission called budding. 



(c) By growing yeast for a few days on a moist slab of 

 plaster-of-Paris under a bell jar or, less successfully in many 

 cases, on the cut surface of a raw potato or carrot some of the 

 cells may be found to have produced four cells by internal cell 

 division. 



(d) Make a very thin cross-section through a young flower 

 bud, or moss capsule. In the stamens of the former or in the 

 interior of the latter, if they are at the right stage, will be found 

 cells which have divided internally into four parts which sub- 

 sequently become spores, each with a thick wall of its own. 



(e) Take a flower bud of Tradescantia just before opening 

 and remove a stamen and mount in water of about the room 

 temperature. By examining with proper manipulation of the 

 light, some cells near the tips of the stamen hairs may be found 

 in division and the main features of the mitotic division of the 

 nucleus may be dimly seen. 



(/) Examine specially prepared, stained sections of rapidly 

 growing root tips, stamens, etc., where cell divisions are taking 

 place frequently. Find and study as many stages as possible 

 of the mitotic division of the nucleus and cells. These prep- 

 arations require especial technique and cannot be made 

 successfully by the beginning student. It is desirable that he 

 study good preparations. Such can be obtained of various 

 supply houses if the teacher has not the time or desire to make 

 them. 



(g) Cell formation by union can be observed in the conjuga- 

 tion of pond scums (Spirogyra or Zygnema) or of black molds 

 (Mucoraceae, especially Sporodinia, which is frequent on 

 decaying toadstools and can be transferred to bread where it 

 grows luxuriantly). 



