PLATE I.-GLCEOCAPSA, OSCILLATORIA, SCYTONEMA, RIVULARIA, NOSTOC, PALMELLA, 



EUGLENA, and YEAST. 



{Figs. 16, 5, ami (5ft after Lwersten; Pirrs. 3 and 4 after Dr Wehcit*ch.) 



Gloeocapsa. 



Glceocapsa (Gr. gffa, glue ; capsa, a case) occurs in damp places, and may be conveniently had for examination from the glass of 

 damp green-houses, where it forms in gelatinous masses. 



The single rounded cell consists of a small protoplasmic mass surrounded by a gelatinous cell-wall, and divides in all the directions 

 of space till it forms a little colony. Division takes place within the parent envelope, and each daughter-cell forms for itself a new cell- 

 wall. The original envelope, stretched in this way, absorbs more and more water until, towards the exterior, it gradually shades off into 

 the surrounding liquid. 



Fig. la. Examine under highest power: \st, as it naturally occurs; 2nd, stained with magenta; and $rd, with iodine to bring out 

 cell-wall distinctly. 



The young cell stains deeply, showing the protoplasm to be dense; the next is undergoing division lengthways, 

 and the third shows transverse division. 



Fig". lb. Showing different stages of division, ending in the formation of a colony. 



Oscillatoria. 



Oscillatoria (so named from its oscillating or pendulum-like movement) occurs in various situations, either in water or on damp 

 earth ; but it may be found at any season of the year by the roadside, where it forms those spreading green patches at the bottom of 

 damp walls, etc 



Under the microscope it is seen to consist of long filaments, each with a distinct colourless sheath of cellulose, containing proto- 

 plasm coloured bottle-green. The protoplasmic contents are marked by transverse lines, with alternate lines only faintly indicated. The 

 power of growth is equally distributed over the whole filament, and any one of the segments can divide into two new ones. 



Under the influence of light these filaments exhibit movement They have a slow, swinging movement from side to side, the stiff 

 filament giving the idea of a pendulum in motion. 



Fig. 2a. Mount a small quantity in a drop of water, and examine under highest power. 



Long filaments, with their contents divided by numerous transverse lines. 



Fig. 2 b. Press upon cover-glass so as to crush the filaments. 



The contents are seen to be little discs wrapped in a sheath of cellulose, which lies about ruptured. 



Fig. 2c. The faint lines between the more decided transverse markings are the expression of the incipient division of each disc 

 into two. 



At the base a single disc is shown. 



Fig. 2d. The moving filament swings from side to side, at the same time going forward. 



Scytonema. , 



Scytonema (Gr. sfa/tos, a whip; nana, a thread) occurs usually in dense tufts on moist rocks, sometimes in sufficient quantity to 

 disguise the natural brownish or blackish colour of the rocks. This particular kind is of a shining black colour. 



Instead of growth going on regularly throughout the filament, as in Oscillatoria, there are some points at which growth is more 

 vigorous, and this bulging gives rise to side filaments or branches. 



Fig. 3. Shows a small tuft in its natural size. 



Fig. 4. Shows a small filament magnified. There is the common sheath wrapping round the discs, and branches going off at 

 particular spots. 



Rivularia. 



Rivularia (I^at. rivulus, a rill) may be found in mountain streams, coating the surfaces of submerged stones or water-plants. It 

 forms dark-green cushions, which are often incrusted with carbonate of lime, thus giving the whole a peculiar hardened look. 



It departs from the uniform characters exhibited by the plants already considered in several respects. 1. Whereas, in Oscillatoria, 

 the filaments of jointed protoplasm could evidently go on growing to any extent, here growth seems to die out at one end, giving rise 

 to a tapering whip-lash filament 2. Whereas, in Oscillatoria, the filaments were of equal diameter throughout, here not only is there a taper- 

 ing at one end of the filament, but there is a globular development at the other end, in the form of a Basal-cell or Heterocyst, incapable 

 of further sub-division. 3. Whereas each segment of Oscillatoria had the power of division, and a detached disc could give rise to a 

 new plant, here certain cells, in the course of a filament, only possess that power. One of the cells becomes a basal-cell, and the cell 

 immediately above that grows out into a new filament As the whip ends of the filaments are all directed outwards, there is a radi- 

 ating appearance presented, with a basal-cell at the bottom of each filament 4. The large cell above the basal-cell may grow till it is 

 fully ten times longer than broad, thus becoming capable of persisting during the winter when the rest of the plant has decayed, and 

 producing a new Rivularia in the spring. 



Fig. 5. A single filament with Basal-cell or Heterocyst (Gr. heteros, different) at one end, and pointed cell at the other. 



The Common Nostoc. 



The Commom Nostoc is to be looked for after rain, as it readily dries up. It occurs as dark, shapeless, jelly-like masses on 

 garden walks or grass plots. 



Under the microscope there is seen to be imbedded in the jelly long convoluted filaments, composed of little globular cells, forming 

 a beautiful beaded neck-lace arrangement, with larger cells every here and there — the Heterocysts. The neck-lace is composed ot 

 distinct cells, and not mere discs of protoplasm embedded in a sheath, as in Oscillatoria. The embedding jelly is probably the cell- 

 walls softened with excess of water and run together. 



The mode of multiplication varies. The portion of the old colony, between two heterocysts, breaks away from the jelly, and in the 

 water the cells stretch themselves transversely and divide repeatedly, parallel to the long axis of the chain. In this way a number of 

 short filaments are formed, side by side, which afterwards arrange themselves end to end, and so form the long meandering chain. In 

 rare cases spores are formed generally between two heterocysts, and persisting after the rest of the filament has decayed, they give rise 

 to a new chain. 



Fig. 6 a. Examine small portion of the jelly under highest power, and observe the beautiful twistings of the chain, with larger 

 cells occurring at intervals. 



Fig. 6b. Stain with Iodine and Sulphuric acid to show the cellulose coat investing each celL 



