59 



banks of tidal rivers are often coloured a light brown, for 

 miles together, by their presence. The almost boundless 

 variety and elegance of form by which Desmids and Diatoms 

 are characterised, together with the great beauty of the 

 sculptured siliceous coat, by which the latter are enveloped, 

 have always rendered these tiny plants favourite objects for 

 the microscope. 



A step higher in the scale is occupied by the Oscillatoria. These 

 are filamentous in their structure, the filaments (as the name 

 Oscillatoria implies), being endowed with a peculiar wavy 

 motion ; the different parts bending from one side to the 

 other with a never ceasing action. Indeed this capability of 

 motion is one of the most singular and most mysterious 

 characteristics of these minute organisms. For all or nearly 

 all of them possess it, either in the whole plant, or some 

 portion of it. The hair-like filaments of the Oscillatoria, as I 

 have just said, wave to and fro with a slow graceful motion : 

 the filaments of Nostoc are also said to have a slight movement 

 in water, but I have never seen it myself, though I have 

 often examined them. In another nearly allied section 

 the Yolvocinea, the members (which are globular in form), 

 swim merrily in their drop of water, and as they at the same 

 time revolve on their own axis, the sight is one to be 

 remembered. Not less interesting is the passage of a Desmid 

 or a diatom across the field of the microscope, conducted 

 however in a much quieter and more sober fashion than are 

 the wild gambols of volvox and its near relatives. A Diatom, 

 whatever its form, moves steadily through the water, turning 

 neither to the right hand nor to the left. If it meets with a 

 fellow diatom or with any like obstacle (as is often the case), it 

 pushes blindly on until the obstacle is removed, or it is itself 

 shunted on one side, in which case its apparently purposeless 

 journey is again resumed. What the object of this gift of 

 motion may be or how it is effected, is entirely unknown. All 

 sorts of conjectures have been indulged in and theories raised, 

 each one in turn to be laid aside. Anyone, however, with a 

 decent microscope may watch the process I speak of at almost 

 any season of the year, and he would prove a genuine 

 benefactor to science, who succeeded in penetrating the mystery 

 of motion in these lowly organisms. 



The case is different with the higher Algae, among which 

 the specimen before us may be reckoned. Here the plant 

 itself is at rest, rooted (or rather^^eJ, for it has no proper 

 roots) to some bulkier object. In lieu of itself being a 

 wanderer, the plant discharges from special receptacles a vast 

 number of Zoospores, which I may liken for simplicity's sake 

 to th.Q seeds of more highly developed plants ; though in reality 

 there is no sort of analogy between them. These Zpo|poyes 



