HANDBOOK OF SEA-WEEDS. 9 



than its form. Each of the cells forms within itself an enormous 

 mass of small elliptic grains. These become attached by the 

 extremities so as to form a network inside the cell, and, its walls 

 being dissolved, a new plant is set free to grow to the size of the 

 parent Hydrodictyon. 



The Nostochinese grow in fresh water, or attached to moist 

 soil. They consist of slender, beaded threads surrounded by a 

 firm jelly, and often spreading into large, wavy fronds. The 

 larger beads on the inclosed threads are reproductive spores. 

 (Fig. 4, A.) 



The Oscillatoreae are another remarkable group, on account 

 of the peculiar animal-like motions they exhibit. They occur 

 both in salt and fresh water, and on almost every kind of site 

 in which there is sufficient moisture. The threads of which they 

 are composed are jointed, and generally unbranched ; they are 

 of various tints of blue, red, and green, and, where their fructifi- 

 cation has been ascertained, are propagated by cell division. 



JS 



:vi: :! i.- 



Fig. 4. A, Fragment of a Filament of Nostoc. B, End of 

 a Filament of Oscillatoria. 



The most curious point about them is, however, the movements 

 of their fronds. According to Dr. Harvey, these are of three 

 kinds a pendulum-like movement from side to side, per- 

 formed by one end, whilst the other remains fixed, so as to form 

 a pivot ; a movement of flexure of the filament itself, the oscil- 

 lating extremity bending over from one side to the other, like 

 the head of a worm or caterpillar seeking something on its line 

 of march ; and lastly, a simple onward movement of progres- 

 sion, the whole phenomenon being, Dr. Harvey thinks, resolv- 

 able into a spiral onward movement of the filament. Whatever 

 is the cause of this motion, it is not, as used to be supposed, 

 of an animal nature ; for the individuals of this group are un- 

 doubted plants. (Fig. 4, B.) Several species of Rivularia, 

 belonging to the Oscillatoreoe, are found both in the sea and 

 in fresh water. They are gelatinous, and have something of the 

 appearance of Nostoc, in aspect as well as in minute structure. 

 The Conjugate are freshwater articulated Algae, which repro- 



