CHAP, i The Cell 173 



being driven by surface tension forces into the angles 

 formed at the points where the foam droplets come into 

 contact. 



The disposition of the protoplasm in the cell cavity and 

 its relation to the vacuolation of the cell, present problems 

 which are mainly physiological and may therefore be 

 deferred. Some discussion took place as to the rela- 

 tions between the external layers of the protoplasm, and 

 the watery contents of the vacuoles on the one side and 

 the cell walls on the other. Hanstein in 1870 first recog- 

 nized that the free surfaces of the living substance, whether 

 bounded by the vacuole or the cell membrane, possess 

 a denser constitution than the rest. The name ectoplasm 

 was applied to these limiting layers as distinct from the 

 endoplasm within them. In all the fibrillar or reticular 

 hypotheses this difference of consistency was explained by 

 relative closeness of mesh or approximation of fibrils on 

 any free surface. This was particularly emphasized by 

 Schmitz in 1882 and by Strasburger in 1882 and 1884. 

 Schneider suggested that they are actually bound together 

 by a special cement substance. 



Biitschli explained them differently. He said that the 

 alveoli, which are situated close to the outside of the 

 protoplasm, are always directed vertically to the surface, 

 so that a radially striated, very thin layer of them is formed. 

 It is not apparently a special kind of membrane at all. 

 Biitschli held that such a layer must occur on the outside 

 of a foam a marginal alveolar layer, and that it may 

 become solid or nearly so and develop into a firm membrane. 



Pfeffer held different views upon the character of the 

 exterior of the protoplasmic unit. He suggested in his 

 Pflanzenphysiologie that definite membranes are produced 

 on the freshly-exposed surfaces of the living substance on 

 their coming into contact with water or some other medium. 

 These are consequently not protoplasmic, but are composed 



