HOMOGENEOUS PROTOPLASM. 89 



The name applied by Mohl to the colourless or yellowish, 

 smooth or granular viscid substance, of nitrogenous con- 

 stitution, which constitutes the formative substance in the 

 contents of vegetable cells, in the condition of gelatinous 

 strata, reticulated threads and nuclear aggregations, &c. 

 It is the same substance as that formerly termed by the 

 Germans ' schleim,' which was usually translated in English 

 works by 'mucus' or * mucilage."' The surface of this 

 mass constituted the "formative protoplasmic layer" a 

 protoplasmic pellicle, which was supposed to take part in 

 the formation of the cellulose wall of the vegetable cell. 

 This protoplasmic layer was regarded by Von Mohl as a 

 structure of special importance distinct from the cell con- 

 tents, and it was named by him, in 1844, the "primordial 

 utricle." The more solid portions of the cell-contents have 

 been regarded as a sort of shell or skeleton for supporting 

 the softer protoplasmic matter that intervened. 



In some cases where protoplasm appears as a simple 

 transparent homogeneous substance, several layers have 

 been described, and it has been supposed that these dif- 

 ferent layers are concerned in different operations. This 

 view has been extended to many forms of protoplasm, and 

 the active movements which characterise certain forms have 

 been attributed to the presence of two or more such layers 

 differing in density. 



Clear, homogeneous protoplasm, it has been said, under- 

 goes " vacuolation" and becomes honeycombed, the spaces 

 being filled with watery matter. In some instances, this 

 change proceeds until mere protoplasmic threads are seen 

 stretched across the cavity. The transparent fluid material 

 occupying the spaces and the intervals between the threads 



