courageous and laconic statement that "Nothing is positively 

 known about the role of the chondriosomes". 



Controversial matters Guilliermond handles with fairness and 

 dignity. Each problem is dealt with unemotionally. He refers to 

 SCHLEIDEN "as the promulgator of the cell theory" ; to Robert 

 HOOKE as the first to recognize the cellular organization of living 

 things, but the significance of this structure was not understood 

 for a long time thereafter. 



I anticipated a rather orthodox cytological handling of the sub- 

 ject by Guilliermond, and so was pleased to find him as awake 

 to the contributions of the newer cytology as to those of the old. 

 He takes de Jong's concept of cytoplasm as a coacervate and applies 

 it to chondriosomes; vesiculation indicates that they too are 

 coacervates. 



Guilliermond deals with the question of the physical nature of 

 the tonoplast. I should like to restate it somewhat differently, and 

 what I say of it is also true of the outer surface layer of proto- 

 plasm. All protoplasmic surfaces are probably coated with fats 

 or other substances which are immiscible with water, but this 

 does not mean that cell membranes are made of any substance 

 other than protoplasm. Cell membranes are immiscible with water 

 because protoplasm is immiscible with water. The immiscibility 

 of protoplasm in water is not primarily due to an oily surface. 

 Structural continuity is responsible. Protoplasm takes up water 

 just as does a sponge, silica gel, or gelatine. Living matter is not 

 a solution of salts, sugars, and proteins. Protoplasm holds to- 

 gether. It could not be a living system if it did not do so. Such 

 misunderstandings have arisen because protoplasm shows certain 

 properties of liquids, such as rounding up and flowing. To certain 

 students this can only mean that protoplasm is a liquid, and if it 

 is a liquid it must be a solution. The colloidal viewpoint clarifies 

 all this. Protoplasm does flow and therefore it is a liquid, but it 

 is elastic, possesses tensile strength and contractility, and imbibes, 

 that is to say, soaks up water. These are the properties of solids, 

 their presence in protoplasm indicates structural continuity. 



Protoplasmic membranes, whether the inner tonoplast or the 

 outer cell membrane, are of living matter, capable of the same 

 physical and chemical changes as is the protoplasm which they 

 bound. The cell membrane is not an inert layer of oil; it is a 

 dynamic living system. 



When amoebae and slime molds move forward, the advancing 

 surface is in a constant state of change. As the surface increases 

 in area, material is added from the inner protoplasm, and as it 

 decreases in area part of its substance is returned to the inner 

 protoplasm. In short, the membrane is protoplasm. Convincing 

 evidence of this is an interesting observation which led one of my 

 students to flatly deny the existence of the tonoplast when it should 

 have caused him to recognize that protoplasmic membranes are 

 alive ; that they are dynamic not static systems. He had observed 

 a particle within the vacuole of a plant cell moving at the same 

 rate and in the same direction as the streaming protoplasm. Close 

 observation revealed that not only the mass of protoplasm but its 



