STRUCTURE OF PROTOPLASM. 319 



is for the complex chemical activities and interchange of sub- 

 stances which go on in the developing egg and growing embryo. 

 In accordance with this is the fact that normal passive protoplasm 

 in mature eggs of Fucus and Echinarachnius ova is quite viscous. 

 (In ripe and resting seeds the protoplasm becomes almost solid.) 



There is no reason for believing that any living protoplasm 

 is naked. The surface membrane of protoplasm is at all times 

 a definite morphological structure. The capacity to form such 

 a pellicle is one of the characteristic properties of the living sub- 

 stance and is retained to a very late stage in dying protoplasm. 



The membrane formed in repairing a tear is of the same char- 

 acter as the original. This is not true in those instances where 

 the wall is of cellulose, as in pollen-tubes and plant embryos; for 

 the enclosing surface layer of protoplasm is but a transformed 

 portion of the living substance, the result of an immediate con- 

 version of liquid plasma into a rigid gel of greater molar concen- 

 tration. (Pfeffer, 1891, p. 194). It is worthy of note that 

 protoplasm possesses not only the capacity to form a membrane 

 but that kind of a membrane characteristic of a particular or- 

 ganism or of a particular stage of development. This suggests 

 that the process is to some degree controlled from within. 



That contact with a certain medium is not necessary for mem- 

 brane formation is evidenced from the fact that streaming myx- 

 omycetes form membranes whether dissected on a dry coverslip 

 or in a hanging drop, and that the pellicle of the Fucus ovum is 

 repaired whether it is torn open in the jelly-mass of the oogonium 

 or in sea-water. Thus does it appear that contact with some 

 medium is not a prerequisite to membrane formation, the lack of 

 a membrane being the stimulus. Membranes are formed on 

 any free protoplasmic surface. The general belief is that this is 

 a purely physical process, and owes its origin to surface forces. 

 It is somewhat disturbing to this strictly mechanistic conception 

 that the capacity for membrane formation ends with death. 

 (Pfeffer (1877) has shown experimentally that a membrane may 

 be formed after death. Chemistry could give us many such 

 instances. In neither case is the membrane a natural one.) 

 Surface forces certainly come into play, but the capacity for 

 membrane formation, and beyond doubt the factor determining 



