230 PROTOPLASM 



haviour of the vacuoles, in the simplest manner, by the 

 physical laws of fluid masses. We can completely grasp 

 the reason why every vacuole must be surrounded by a 

 continuous pellicle-like border, which shuts it off from the 

 neighbouring layer of alveoli. We understand their spherical 

 form, their occasional flowing together, etc., in the easiest 

 manner ; but we can comprehend a great deal more, 

 which the framework theory is unable to explain. That is 

 to say, we can understand why each vacuole is surrounded 

 by a radially arranged layer of alveoli, as has been shown 

 above in a series of examples. For this point the frame- 

 work theory is not able to furnish a solution. 



I must not leave entirely without mention in this place a 

 theory of the vacuoles which has sprung up on botanical grounds, 

 and has found numerous adherents among botanists, namely, de 

 Vries's Tonoplast Theory. De Vries is, as is well known, of the 

 opinion that the vacuoles are just as much independent organs of 

 the cell as the cell nucleus, the chromoplasts, and other things. 

 The vacuoles are the products of so-called tonoplasts, certain small 

 bodies which build up strongly osmotic substances within them- 

 selves, and in this way swell up to vacuoles. The vacuoles always 

 possess, it is supposed, a special, independent membrane, distinct 

 from the rest of the protoplasm, which arises from the tonoplasts, 

 and is to be regarded as the true active and living part of these 

 structures. Admitting the correctness of this view, the difficulty 

 would arise of explaining the continuous limitation of the 

 vacuole. I regard, however, de Vries's theory as on the one hand 

 unproved, in fact improbable, and on the other hand I consider 

 the origin of the vacuoles to be completely intelligible without 

 the tonoplast theory. 



In the first place, there is a lack of any substratum of fact for 

 the assumption of tonoplasts. No one has ever seen them in the 

 non-vacuolated condition ; there is therefore a necessity for other 

 grounds upon which to justify the assumption. Among such it 

 would of course be decisive to show that the vacuoles were only 

 formed like the nucleus or the chromoplasts, by multiplication 

 on the part of bodies like themselves. Now de Vries is actually 

 of the opinion that this multiplication always occurs. What, 

 however, he brings forward (1886) in the way of facts cannot 

 be regarded as the slightest proof of an independent multipli- 

 cation of the vacuoles, but would rather seem to be entirely 

 a case of constriction of larger vacuoles into smaller ones 



