24:8 



THE MICROSCOPE AND ITS REVELATIONS. 



According to Dr. F. d'Alquen, 1 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 

 colorless when moist, though slightly greenish when dry. And he gives 

 reasons for the belief that it is in this (protoplasmic?) axis that the pecu- 

 liar motor power of the filament specially, if not exclusively, resides. 

 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, however, with blue; 

 but not infrequently 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 

 movements are described by Dr. Harvey 3 as of three kinds; first, a pen- 



Formation of Zoospores in Phycoseris gigantea (Ulva latissima) : a, portion of the ordinary- 

 frond; 6, cells in which the endochrome is beginning to break up into segments; c, cells from the 

 boundary between the colored and colorless portions, some of them containing zoospores, others 

 being empty; d, flagellated zoospores, as in active motion; e, subsequent development of the zoo- 

 spores. 



dulum-like movement from side to side, performed by one end, whilst 

 the other remains fixed so as to form a sort of pivot; second, a movement 

 of flexure of the filament itself, the oscillating extremity bending over, 

 first to one side and then to the other, like the head of a worm or cater- 

 pillar seeking something on i.ts line of march; and third, a simple onward 

 movement of progression. " The whole phenomenon," continues Dr. H., 

 " may perhaps be resolved into a spiral onward movement of the filament. 

 If a piece of the stratum of an Oscillatoria be placed in a vessel of water, 

 and allowed to remain there for some hours, its edge will first become 

 fringed with filaments, radiating as from a central point, with their tips 

 outwards. These filaments, by their constant oscillatory movements, are 

 continually loosened from their hold on the stratum, cast into the water, 



1 " Quart. Journ. of Microsc. Science," Vol. iv. (1856), p. 245. 



2 " Manual of British Marine Algae," p. 220. 



