THALLOPHYTES 



41 



and characteristically shaped chloroiilasts. There is no asexual repro- 

 duction by spores, and no motile cells of any kind are formed. Sexual 

 reproduction is effected by the conjugation of protoplasts brought 

 together usually through conjugating tubes, and while in a general way 

 only isogamy is attained, there is evident in some forms an incipient 

 heterogamy shown by the different behavior of the pairing protoplasts. 

 The group as a whole seems to stand stiflEly apart from all those previ- 

 ously considered, and must be regarded as very highly speciahzed. 



(f) Charales 



General character. — The stoneworts, as these forms are called, con- 

 stitute a very isolated group among thallophytes, which seems to hold 

 no definite relation to any other 

 group. If they are algae, they 

 must be included among the 

 green algae ; but they are con- 

 sidered by many to be quite 

 separate from algae ; and some 

 would even remove them from 

 thallophytes. Until something 

 more is known of their relation- 

 ships, however, it is convenient 

 to consider them in connection 

 with the green algae. They are 

 found in fresh and brackish 

 waters, attached to the bottom 

 and covering large areas with a 

 dense mass of vegetation. Some 

 of the bodies are incrusted by 

 such an abundant deposit of 

 calcium carbonate that it makes 

 them rough and brittle, and sug- 

 gested the name stoneworts. 

 The common genera are Chara 

 and Nitella, and the general 

 structure is very uniform. 



Vegetative body. — The vegetative body consists of a cyUndric stem or 

 main axis which branches profusely (fig. 113). All of the axes are dif- 

 ferentiated into short nodes and long internodes, and from the nodes the 



Fig. 113.- 



- Chara: showing general habit 

 of body. 



