VII] CHARA. 223 



The Oharophyta are plants containing chlorophyll, living in 

 fresh and brackish water ; the stena is jointed, and bears at the 

 nodes whorls of leaves, on which are borne the reproductive 

 organs. The antheridia are spherical in shape and of complex 

 structure, containing numerous biciliate antherozoids. The 

 oogonia are oval in form and contain a single large egg-cell. 

 The Chara-plant is developed from a protonema formed from 

 the germinating oospore. Vegetative reproduction is effected 

 by means of bulbils, accessory shoots, etc. 



The NitellesB have not been recognised in a fossil condition. 

 The absence or feeble development of a calcareous incrustation 

 renders the genera of this family less likely to be preserved 

 than such a genus as Chara. 



Chareaa. 



Leaves and stems with or without a cortical investment. 

 Fruit with a five-celled corona. The envelope of the ' fruit ' 

 and other parts of the plant are frequently encrusted with 

 carbonate of lime. 



In the genus Chara, the best known member of the family, 

 the plant as a whole resembles in its general habit and external 

 differentiation of parts the higher plants. The stem consists 

 of long internodes separated by short nodes bearing whorls of 

 leaves. Each intemode consists of a long cylindrical cell, which 

 becomes enclosed by a cortical sheath composed of rows of cells 

 which have grown upwards and downwards from the peripheral 

 nodal cells. The cortical cells are usually spirally twisted and 

 impart to the stem a characteristic appearance ; they are divided 

 by transverse walls into numerous cells some of which occasion- 

 ally grow out into short processes (fig. 45 c). The leaves repeat 

 on a smaller scate the structural features of the stem, but 

 possess a limited growth, whereas the stem has an unlimited 

 power of growth by means of a large hemispherical apical cell. 

 Branches arise in the axils of the leaves. The plants are either 

 monoecious or dioecious. The oogonium is elliptical in shape, 

 and is borne on a short stalk-cell, it contains a single oosphere. 

 The wall of the oogonium is formed of five spirally twisted cells 

 which have grown over it from the five peripheral cells of a 



