THE CHAROPHYTA 



379 



Chara fragilis (The Stonewort) 



The plant grows to a height of about a foot, though some other species 

 are considerably smaller (Fig. 363). It consists of an erect, somewhat 

 sparsely branched stem, which bears 

 whorls of short lateral branches pro- 

 duced at nodes, which consist of a 

 transverse layer of small cells. The 

 internodes between them are either 

 made up of a single giant cell, or 

 composed of a single central cell sur- 

 rounded by a number of peripheral 

 cells, which grow over it and are de- 

 rived from the nodes above and below. 

 The laterals themselves are of limited 

 growth and often produce shorter second- 

 ary laterals, so that the whole structure 

 comes to resemble an Equisetum ; which 

 accounts for the fact that as early as 

 1660 John Ray regarded the group as 

 aquatic Horsetails. 



Growth is brought about by means 

 of a dome-shaped apical cell, which 

 cuts off a series of segments parallel 

 to its flat base (Fig. 364). Each segment 

 divides horizontally into two cells, of 

 which the upper gives rise to a node 



and the lower to an internode. The nodal cell divides into a series of cells, 

 consisting of a definite number of peripheral ones and a small number, 

 generally two, central ones. These peripheral cells then function as apical 

 cells and form the lateral branches of limited growth. The number of 

 these laterals is therefore determined by the number of peripheral segments, 

 and is a constant for each species. Each lateral now develops by the division 

 of its apical cell in a way identical to that of the main stem, but the internodes 

 remain relatively short, and the whole branch is of strictly limited growth. 

 The secondary laterals which it produces are shorter still, and in both cases 

 the apical cells soon cease to divide and then elongate, forming pointed 

 terminal cells. In successive whorls the individual laterals alternate. 



Branches of unlimited growth arise from the lowest or basal cells of 

 the first node formed on the laterals of limited growth, and it is also from these 

 cells that the cortications arise which cover the internodal cell of the main 

 stem (Fig. 364). Such cortications are characteristic of all species of Chara. 

 The cortications arise from cells of the basal branch-node, which divide to 

 give a series of small cells, some of which grow upwards over the internodal 

 cell of the internode above, while the others grow down over the internodal 

 cell below. As they develop they not only keep pace with the elongation of 



Fig. 363. — Chara fragilis. Vegetative 

 shoots with branches. Natural size. 



