VI. 



STONE WORTS {Chara and Nitdla). 



These water-weeds are not uncommonly found in ponds and 

 rivers, growing in tangled masses of a dull green colour. Each 

 plant is hardly thicker than a stout needle, btit may attain a 

 length of three or four feet. One end of the stem is fixed in the 

 mud at the bottom, by slender thread-like roots, the other floats 

 at the surface. At intervals, appendages, consisting of leaves, 

 branches, root- filaments, and reproductive organs, are disposed 

 in circles, or whorls. In the middle and lower parts of the 

 plant these whorls are disposed at considerable and nearly 

 equal distances ; but, towards the free upper end, the intervals 

 between the whorls diminish, and the whorled appendages 

 themselves become shorter, until, at the very summit, they 

 are all crowded together into a terminal bud, which requires 

 the aid of the microscope for its analysis. 



The parts of the stem, or axis, from which the append- 

 ages spring are termed nodes ; the intervening parts being 

 internodes. When viewed with a hand-magnifier the inter- 

 nodes exhibit a spiral striation. 



In Chara, each intern ode consists of a single, much-elongat- 

 ed cell, which extends throughout its whole length, invested 

 by a cortical layer, composed of many cells, the spiral ar- 

 rangement of which gives rise to the superficial marking 

 which has been noted. And this multicellular structure 

 is continued from the cortical layer, across the stem, at each 

 node. The stem therefore consists of a series of long, axial 

 cells, contained in as many closed chambers formed by the 



