110 



THE SCIENCE OF LIFE. 



but may be three or four feet long. It has rootlets 

 springing from the axis, by which it is fixed in the 

 muddy bottom of the stream, etc., but the main source 

 of its nutriment is the water in which it lives. It pos- 

 sesses chlorophyll, and in consequence decomposes car- 

 bonic acid under sunlight, retaining the carbon to form 

 part of its own substance, and giving off the oxygen. 

 The branchlets (or leaves, as they are called) are grouped 

 in whorls, or spring from the same height in the stem. 



FIG. 39. Nitella flexilis : A. Stem and branches of the natural size. a. b. c. d. Four 

 verticils of branches issuing from the stem. e.f. Subdivision of the branches. B. Portion 

 of the stem and branches enlarged, a. b. Joints of stem. c. d. Verticils, e.f. New cells 

 sprouting from the sides of the branches, g. h. New cells sprouting at the extremities of 

 the branches. 



and at regular intervals. (Fig. 39.) The main stem is 

 called the axis, and a branch, when it exists, is a second- 



