R. BRAITHWAITE ON TFIE HISTOLOGY OF PLANTS. 133 



pass tlirough tlie cell sap. When the cell nucleus is embedded in 

 the wall-plasma, then the separate vacuoles unite into a single 

 central vacuole, which becomes the whole inner cavity of the cell 

 occupied bj the cell sap, and only in rare cases a few fine proto- 

 plasm threads stretch across from wall to wall. In the very young 

 first-formed cell the protoplasm aj^pears quite uniform, and as a 

 finely granulose semi fluid. The next stage is a separation into 

 two layers, one, almost quite homogeneous and viscid, lies close to 

 the primordial membrane ; the other, more fluid and granulose, 

 stands between the outer layer and the central fluid. This inner is 

 named by Pringsheim the granular layer, and is usually more 

 abundant than the outer layer ; in it also lie the nucleus, chloro- 

 phyl, &c. 



One of the most interesting phenomena of cell life is the move- 

 ment of the granular protoplasm, observable in all young living 

 cells, and this, moreover, takes place in two directions. We may 

 detect — 1st, a ^jcirietal current where the stream follows the outline 

 of the cell wall, either simply ascending and descending, or cross- 

 ing spirally, or branching in a net-like form ; 2nd, an internal cur- 

 rent, which extends along the protoplasm threads, crossing the 

 lumen, or clear central space of the cell. 



The simi3le parietal current is exemplified by the well-known 

 cyclosis or circulation in Nitella and Vallisneria, and is also well 

 seen in the hair-like radicles of the Hydrocharis morsus rancB, or 

 Frogbit, and less readily in Naias, Closterium, &c. 



A single spiral parietal current may be observed in the hairs 

 from the ovary of various species of CEnothera, and in elongated 

 cells from the young flower- stalk of Tradescantia Virginica, and 

 also in young cells of jointed hairs from stamens of the latter 

 plant. More complicated spirals are well seen in the young elaters 

 of liver -mosses. A reticulate, branching current can only be ob- 

 served at the commencement of similar formed thickening layers of 

 vessels and cells. 



The internal current passes to and from the cell nucleus ; a 

 variable number of simple or anastomosing streamlets of granular 

 stratified protoplasm run across on the inner side of the cell wall, 

 or through the lumen of the cell, returning immediately to the 

 nucleus, and after repeated gyrations, uniting with the protoplasm 

 enclosing it. This phenomenon may be observed in every young, 

 recently-impregnated germ-cell, in the commencing cells of paren- 



