CHAPTER X 



THE CHAROPHYTA 



The Charophyta are a small but important group of plants which show 

 marked differences from both the Thallophyta and the Bryophyta. 



They are all specialized water plants with a highly peculiar structure 

 and complex reproductive organs. Chlorophyll is the only pigment they 

 possess, and they may be related to the Chlorophyceae ; in fact some 

 authorities have relegated them to that group as a separate order. The 

 older view, and one which still has much to recommend it, was to regard 

 them as a separate phylum, of equal rank with the Thallophyta, whose 

 relationship to other phyla was unknown. 



The species are distributed throughout the world, but are most common 

 in the warm and cool temperate zones. It may be mentioned that plants 

 with a wide geographical distribution are often known to be of greater 

 antiquity than those of restricted distribution, and the Charophyta are 

 no exception to this rule, for remains of them are found as far back as the 

 Devonian and Carboniferous rocks. Such forms differ little from the 

 present-day types and throw no light on the ancestry of the group. 



Because of the fact that they are common and widely distributed they 

 have been known from early times and were used by many early botanists 

 as material for study and demonstration. For example, the cyclosis of cyto- 

 plasm was first demonstrated in the cells of Chara by Amici in 1818. 



The Charophyta are plants whose stems are either green or grey; the 

 latter occurs in many species, resulting from the masking of the green colour 

 by incrustations of lime on the w'alls. The main stems are slender and 

 slightly branched. Lateral branchlets occur in whorls at regular intervals 

 up the stem. The reproductive organs consist of antheridia and oogonia, 

 though the structure of these organs differs considerably from the 

 corresponding organs in the Algae. As a result of fertilization a protonema 

 is formed from which the sexual plant is developed. 



The plants are submerged, and occur widely in fresh water or water con- 

 taining less than i per cent, of salt. Thus they are found in the Baltic Sea, 

 but not in other more saline waters. The water must be still, or only slow- 

 flowing. There must be no pollution due to sewage, and the plants must be 

 exposed to bright light. They are frequently found in water charged with 

 calcareous material. 



The phylum contains only one family, Characeae, with six genera and 

 about two hundred species. We shall consider only one example, Chara 

 fragilis ; since the differences between the genera are small this species 

 may be considered typical of the whole group. 



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