PLATE IV.— PROTOCOCCUS, PANDORINA, ULOTHRIX and HYDRODICTYON. 



Protococcus Vulgaris. 



Protococcus Vulgaris (Gr. protos, first ; kokkos, a berry), or Pleurococcus, is well known as the green scum on the bark of trees. 

 It is so widely diffused that its means of multiplication must be very perfect. In fact it is like a continuous growing point, ever 

 dividing and ever ready to divide. 



Under the microscope it is seen to consist of rounded cells, usually having a nucleus. This nucleus is a denser portion of the 

 protoplasm and stains more deeply than the rest The cells are also seen to be divided into two, three, or four portions. But towards the 

 end of autumn another process of division takes place. The contents of the cell break up into a great number of little masses which, 

 on escaping by the rupture of the cell-wall, are seen to consist of naked bits of protoplasm, with two threads of it propelling them 

 rapidly through the water. This naked moving protoplasm afterwards forms a cell-wall. 



Fig. 1. Take a little bit of the bark of a tree, with this green scum upon it, and scrape off some of it into a drop of water on 

 a slide. Examine under highest power. 



(a.) Ordinary resting-form consisting of Cell-wall and green-coloured contents. 



(b.) Iodine brings out Nucleus — seen as a small dark spot in the centre of the cell. 



Iodine and Sulphuric acid together — the cell-wall becomes blue and the protoplasm coagulates. 



Crushed — to distinguish clearly between the tough cell-wall and the semi-fluid protoplasm. 



Potash — dissolving the protoplasm. 

 (<r.) Multiplication by Division into four. The protoplasm first of all separates into two masses, and cell-wall forms in 



the partition between. Next, each half behaves like the original whole so that four divisions are formed These 



divisions separate, become rounded, and each forms a new Protococcus. 

 (d.) Endogenous Division producing motile forms. The protoplasmic contents begin to divide in the same way as 



before, but instead of stopping at four, there is division into numerous segments of naked protoplasm. The 



particles become rounded and escape as motile forms through the rupture of the original case. The motile 



ciliated forms, non-sexually produced, are called Zoogonidia (Gr. zoon, an animal). 

 In the resting-forms it will be noticed, that they were clothed with a cell- wall before being set free, whereas 

 the motile forms only assume a cellulose covering afterwards. 



Life History. — Multiplication takes place either by simple division into four portions, or into numerous motile forms, which after- 

 wards settle down and return to the ordinary resting-form. 



Protococcus Pluvialis. 



Protococcus Pluvialis (Lat pluvia, rain) as the specific name denotes, occurs in places where rain-water collects. 



Fig. 2. Take some of the mtfddy sediment from rain-water, mount with clean water and examine under highest power. 

 Observe motionless and motile forms. The motile forms may either be clothed with a wall or naked. 



Pandorina. 



Pandorina (Gr. Pandora, a beautiful woman) occurs in ponds and ditches, but it may be had for examination from certain Natural 

 History dealers. 



There are sixteen cells united into a free-swimming colony of globular shape by a gelatinous investment. Each of these sixteen 

 cells may give rise to a new colony. The cilia are withdrawn, whereby the whole comes to rest, and each individual divides into 

 sixteen portions like the parent In other cases, however, a single cell does not reproduce the colony. Two cells from different 

 individuals fuse together and the common mass ultimately forms a young colony. This process is called Conjugation, where the 

 two uniting elements closely resemble each other, and the result of it may be traced in the Figures. 



Fig. 3a. Colony or Ccenobium (Gr. koine, in common ; bios, life) consisting of sixteen cells or Zoogonidia. Each Zoogonidium has 

 a red eye-spot and two projecting cilia, by the collective and harmonious action of them all a rolling motion is imparted 

 to the whole family. 



(b, r.) Male and Female Zoospores. These reproductive cells are produced from different colonies, the smaller 



being reckoned the Male, and the larger the Female element. 

 (d, e.) In conjugation, the two elements first come into contact by their ciliated ends, then they gradually swing 



round side by side and fuse completely. 

 (f,g.) The single body resulting from conjugation is called a Zygospore (Gr. zugos, a yoke; spora, a seed). This 

 zygospore bursts its case and begins to germinate. 

 (h.) The germinating Zygospore draws in its cilia, rounds itself off and divides into sixteen cells, forming a colony. 



Life History. — Each Zoogonidium of the Pandorina-colony -divides into sixteen portions — like the original — and then escapes through 

 the gelatinous wall. This is the non-sexual mode ot multiplication. The sexual reproduction consists in the production of cells 

 which are called Zoospores, one colony forming sixteen small (male) Zoospores, another sixteen larger (female) Zoospores. 

 Two unite to form a Zygospore, which germinates and produces a new colony. 



Ulothrix Zonata. 



(After Dodel-Port). 



Ulothrix Zonata (Gr. oulos, woolly or curly; thrix, hair), or Curly-hair Alga, may be found in fresh waters, such as brooks, drink- 

 ing fountains and the like. It occurs in green tufts attached to some fixed body. 



It is a simple filamentous Alga, reproducing itself non-sexually during winter and sexually during summer, but if the sexually reproduc- 

 tive cells fail to conjugate, they may still grow into a new plant 

 Non-sexual Stage — 



Fig. 4. Portion of Filament in vegetating condition. 



The cylindrical cells are placed end to end, and in each there is a green protoplasmic band about the 

 middle containing a nucleus. 



Fig. 5. Portion of Filament exclusively producing Zoogonidia. 



A mother-cell may produce one, two, four, or eight zoogonidia. The inner wall of the cell passes out as an 

 envelope surrounding them, and afterwards deliquesces to allow their escape. 



Fig. 6. The Zoogonidium is pear-shaped, with four cilia and a red eye-spot and a contractile vacuole. 

 (a.) In motion, it rotates round its long axis by means of the four cilia. 

 (b.) On coming to rest, the cilia become stiff and fall off, and the zoogonidium fixes itself, by its tapering end, to 



some object 

 (c.) The zoogonidium now germinates and, by repeated division, produces a filament, as in Fig. 4. 



