322 ULVACEvE. — OSCILLATORIACE^E. 



that, a little further still, they are obviously but masses of Endc- 

 chrome in the act of subdivision.* 



242. Of the true Generative process in the Ulvaceae nothing 

 whatever is known ; and it is consequently altogether uncertain 

 whether it takes-place by simple Conjugation, or according to that 

 more truly Sexual method which will be presently described. Here, 

 again, therefore, is an unsolved problem of the greatest Physiological 

 interest, which probably requires nothing more for its solution than 

 patient and intelligent study. And the Author would point out, 

 that it is by no means unlikely that the Generative process may not 

 be performed in the complete plant, but, as in the Ferns (§ 280), 

 in the early product of the development of the Zoospore. — Although 

 the typical Ulvacece are Marine, yet there are several Fresh-water 

 species ; and there are some which can even vegetate on damp sur- 

 faces, such as those of rocks or garden-walks kept moist by the 

 percolation of water. 



243. The Oscillator iacece constitute another tribe of simple 

 Plants of great interest to the Microscopist, on account both of the 

 extreme simplicity of their structure, and of the peculiar Animal- 

 like movements which they exhibit. They are continuous tubular 

 filaments, formed by the elongation of their primordial cells, usually 

 lying together in bundles or in strata, sometimes quite free, and 

 sometimes invested by gelatinous sheaths. The Cellulose coat 

 (Fig. 149, A, a, a) usually exhibits some degree of transverse stria- 

 tion, as if the tube were undergoing division into cells ; but this 

 division is never perfected by the formation of complete partitions, 

 though the Endochrome shows a disposition to separate into regular 

 segments (b, c), especially when treated with re-agents ; and the 

 filaments ultimately break up into distinct joints, the fragments of 

 Endochrome, which are to be regarded as gonidia, usually escaping 

 from their sheaths, and giving origin to new filaments. + These 

 Plants are commonly of some shade of green, often mingled, how- 

 ever, with blue ; but not unfrequently they are of a purplish hue, 

 and are sometimes so dark as when in mass to seem nearly black. 

 They occur not only in fresh, stagnant, brackish, and salt waters 

 (certain species being peculiar to each), but also in mud, on wet 

 stones, or on damp ground. Their very curious movements con- 



* Such an observation the Author had the good fortune to make in the 

 year 1842, when the emission of Zoospores from the Ulvacese, although 

 it had been described by the Swedish Algologist Agardh, had not been 

 seen (he believes) by any British naturalist. 



t According to Dr. F. d'Alquen ("Quart. Journ. of Microsc. Science,' 

 Vol. iv. p. 245), each filament— at least in certain species — has an axis of 

 different composition from the surrounding endochrome ; being solid, 

 highly refractive, but slightly affected by iodine, and nearly colourless 

 when moist, though slightly greenish when dry. And reasons are given 

 by this observer for the belief that the peculiar motive power of the 

 filament resides specially, if not exclusively, in this axis. 



