THE GREEN FELT: VAUCHERIA. 121 



since the organs of reproduction can be readily seen, usually 

 much easier to study than in any of the plants belonging to the 

 higher groups. If fresh material is not at hand, that which has 

 been preserved in alcohol or formalin will serve very well. 

 Often excellent material is to be found in greenhouses growing 

 on the soil of pots during the winter, especially if one obtains 

 from outside in the autumn some bulbs of arisaema (jack-in-the- 

 pulpit) with soil near them for potting. Fresh material of 

 vaucheria in fruit is found easily during the autumn or spring. 

 At this time a quantity should be preserved. The sexual 

 organs are usually more abundant when the threads appear 

 somewhat yellowish or yellow green. 



Exercise 43. 



205. Gross characters of vaucheria. — If fresh material is at hand which 

 was growing in water, note how firmly the threads are tangled together ; 

 compare with spirogyra in this respect. Can you make out in this condition 

 that the threads are branched? This branched condition of vaucheria is 

 one of the reasons for the dense tangle of threads. Note the coarse feeling ; 

 compare with spirogyra in this respect. 



If material on the soil is at hand, note that it is not necessary that all 

 species grow in water. Note here also the dense tangle of threads. Lift up 

 a tuft with the needle ; compare the effect on the threads with that of spiro- 

 gyra when a. tuft of the latter is lifted in the same way. Compare the 

 " feeling " of the threads with that of spirogyra. 



Demonstration 31. 



206. Sexual reproduction in vaucheria. — Mount a few threads of fruiting 

 vaucheria in water for microscopic study. If prepared slides are at hand 

 they will answer for the demonstration. Let each pupil make a sketch of 

 the sexual organs, and make notes of the form of the same ; also note the con- 

 tinuity of the threads, cross-walls* only being formed in connection with the 

 reproductive organs. Let them compare the different stages found in the 

 formation of the ripe egg. 



both kinds of the sexual organs are more easily found and understood, those 

 of oedogonium being more complicated. See Chapters XVI and XVII of 

 the author's larger "Elementary Botany." 



