VI. 

 STONEWORTS (Ckara and Nitella). 



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, but 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, append- 

 ages, consisting of leaves, branches, root-filaments, and repro- 

 ductive organs, are disposed in circles, or whorls. In the 

 middle and lower parts of the plant these whorls are dis- 

 posed 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 internode consists of a single, much- 

 elongated cell, which extends throughout its whole length, 

 invested by a cortical layer, composed of many cells, the 

 spiral arrangement of which gives rise to the superficial 

 marking which has been noted. And this multicellular 

 structure is continued from the cortical layer, across the 



