DISCOVERY OF PROTOPLASM. 



25 



DISCOVEEY OF PROTOPLASM. 



The study of Vaucheria led, then, to the discovery that there are plants which, 

 in the course of their development, pass through a motile stage, propelling them- 

 selves about the water as tiny halls of jelly with ciliary processes, and giving 

 exactly the same impression as infusoria. Hand in hand with this discovery went 

 the further observation that a portion of the plastic cell-contents in all plants lies, 

 like a lining, in contact with the inner face of the cell-walls, so that we find that 

 these latter, at a certain stage of maturity, are made up of two layers lying close 



Fig. 5. —Protoplasm inclosed in Cells. 



i Protoplasm in cells of Orobanche. 2 streaming protoplasm in cells of Vallisneria. 8 Streaming protoplasm 



in cells of Elodea. 



together, the outer one firm and the inner soft. The name of "primordial utricle" 

 was given to this inner layer. On further investigation it turned out that this 

 primordial utricle belongs to a body of gelatinous, slimy consistency which lives in 

 the cell-cavity like a mussel or a snail in its shell. At first it is shapeless and fills 

 the whole cavity with what appears to be a homogeneous mass; but later on it is 

 differentiated into a number of easily- recognizable parts — i.e. into the above- 

 mentioned lining towards the inner surface of the cell-membrane, and into folds, 

 strands, threads, and plates stretching across the interior of the cell. (See fig. 5.) 

 Mohl of Tubingen, the discoverer of these facts, applied in 1846 the name of proto- 

 plasm to the substance of which the cell-contents are composed. 



It is possible for protoplasm, under certain conditions, to exist for a time without 

 any special protective envelope; but, as a general rule, it secretes at once a firm, 



