CHAPTER III 



THALLOPHYTA : ALGAE (CONTINUED) 



8. CHAROPHYCEAE 



The Charophyceae, or stoneworts, constitute a very isolated group of 

 highly organized green thallophytes with uncertain affinities. Although 

 often included in the Chlorophyceae, they are so distinct that they belong 

 in a separate and coordinate class. The Charophyceae are multicellular 

 plants in which the only pigments present are chlorophyll and its asso- 

 ciated carotinoids, these occurring in essentially the same proportions as 

 in the green algae. They include 6 genera and about 200 species, nearly 

 all of which belong to Chara and Nitella. The stoneworts grow in 

 streams, ponds, and lakes attached to the bottom. They also live in 

 brackish water but not in the ocean. Most species of Chara extract 

 calcium carbonate from the water and deposit it in their walls, thereby 

 becoming rough and brittle. Fossils belonging to the Charophyceae 

 have been identified in deposits of the Cretaceous and later geologic 

 periods. There is some evidence of their existence even as far back as 

 the Devonian. 



Vegetative Body. The vegetative body of the stoneworts consists of 

 a slender cylindrical stem bearing many short branches in whorls (Fig. 

 51 A). It grows erect and often reaches a height of 20 to 30 cm. The 

 stem is attached to the substratum by means of colorless branched 

 rhizoids. It is made up of short nodes and long unicellular internodes, 

 the branches arising from the nodes. There are two kinds of branches: 

 branches of unlimited growth, comprising the main axes, and branches of 

 limited growth, the so-called leaves, in whose axils the main axes arise. 

 All the cells contain numerous small spherical chloroplasts without 

 pyrenoids. Reserve food is stored as starch. 



Both kinds of branches grow by means of an apical cell, hemispherical 

 in shape, that cuts off a longitudinal series of segments by successive 

 transverse walls (Fig. olB). Each segment again divides transversely 

 into two cells, the lower one becoming the long internodal cell and the 

 upper one the nodal cell. The latter, by vertical divisions, gives rise to 

 a plate of cells that produce the branches. The internodal cell, often 

 attaining a length of 10 cm., may become coenocytic by fragmentation of 

 its nucleus. Its cytoplasm gives a striking demonstration of protoplasmic 

 streaming. In Chara the internodal cells become ensheathed by cells that 



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