The protoplast 



3 



c 



Fig. 2. Unicellular Blue-green Algae embedded 

 in mucus and showing the colonial habit. A, 

 Aphanocapsa Grevillei (Hass.) Eabenh. ; B, 

 Gloeocapsa magma (Breb.) Kiitz. ; C E, Gl. 

 montana Kiitz. All x 450. 



the layers may be coloured. In the filamentous forms the mucus is in the 

 form of a sheath, which is often 

 readily diffluent, as in Anab&na, 

 many species of Phormidium, etc. ; 

 or it may attain various degrees of 

 toughness and not infrequently 

 become chitinized, as in Lyngbya, 

 Scytonema, etc. Sheaths of this 

 kind are the secretion of the en- 

 closed cells of the filament, and all 

 stages can be observed between a 

 hyaline mucous investment and 

 a tough, lamellose sheathing tube. 

 The strong sheaths of some forms 

 are therefore the homologues of the 

 copious mucous integuments of 

 others. All the gelatinous invest- 

 ments and sheaths originate as 

 lamellae, although this is sometimes 

 scarcely evident, and they should 

 really be regarded as portions of 



the cell- wall, in some cases undergoing gelatinization and in others a 

 toughening to form a hard sheath. The gelatinous mass consists mostly 

 of pectose compounds, and in certain species of Glceocapsa is brilliantly 

 coloured. The investments of the unicells as well as those of the filamentous 

 forms are often chitinized. In a few species of Schizothrix the sheath con- 

 sists partly of cellulose and colours blue with chlor-zinc-iodine. 



The general function of the sheaths and gelatinous investments of the 

 Myxophyceae is undoubtedly to enable the plants to withstand periods of 

 dryness, as the water is but slowly evaporated from such investments, and 

 is very readily absorbed. They thus form a kind of water-reserve. 



THE PROTOPLAST. Much controversy exists regarding the structure 

 of the protoplast. It can readily be seen, sometimes even in the living 

 cell, to consist of two parts, a peripheral coloured zone surrounding a colour- 

 less 'central body.' Both portions are generally granular, the granules of the 

 central body being larger and as a rule only observable by appropriate staining. 

 During the last thirty years this so-called centred body has received much 

 attention from cytologists, largely with the view of determining whether 

 or not it should be considered as a true nucleus with functional activities 

 of a similar nature to those exhibited by the nuclei of more highly organized 

 cells. It occupies in most cases about one-quarter or one-third the volume 



12 



