MORPHOLOGY 



59 



A particularly favourable object for the study of protoplasm in circulation is 

 afforded by the staminal hairs of Tradescantia virginica. In each cell (Fig. 60) 

 small, fine currents of protoplasm flow in different directions in the peripheral 

 cytoplasmic layer, as well as in the cytoplasmic threads, which penetrate the sap 

 cavity. These cytoplasmic threads gradually change their form and structure, and 

 tli us alter the position of the cell nucleus. 



When the protoplasm is in rotation, the cell nucleus and chromatophores are 

 usually carried along by the current, but the chromatophores may remain in the 

 boundary layer, and thus not undergo movement. This is the case with the 

 Stoneworts (Characeae), whose long internodal cells, especially in the genus 

 NiteMa, afford good examples of well-marked rotation. 



Properly fixed cytoplasm has a finely reticulate or honeycomb- 

 like structure, small granules being embedded in the network. 

 At particular developmental stages this structure appears to be 

 traversed by special filaments, which can be demonstrated by suitable 

 staining (Fig. 57) ( 36 ). 



The portion of the cytoplasm which forms the network or honeycomb appears 

 to be specially concerned with the nutritive processes, while the fibrillar plasma 

 influences the process of development ; they are respectively 

 termed trophoplasm and kinoplasm ; the latter has also been 

 called archeplasm. When traced to their origins the limiting 

 layer of the cytoplast is found to belong to the kinoplasm, 

 the walls of vacuoles to the trophoplasm. Albuminous sub- 

 stances, precipitated by the fixing agent, have not infre- 

 quently been mistaken for structural features of the cyto- 

 plasm ( s7 ). 



The Cell Nucleus ( ys ). The resting nucleus 

 has a reticulate or honeycomb structure forming 

 an anastomosing network (Fig. 56), which, how- 

 ever, in living objects can only be distinguished 

 by the punctated appearance it gives to the 

 nucleus. Streaming movements do not take place 

 within the nucleus. An insight into the nuclear 

 structure is only to be attained with the help of 

 properly fixed and stained preparations. It is then 

 possible to determine that the greater part of this 

 nuclear network is composed of delicate and, for 

 the most part, unstained threads, in which lie deeply 

 stained granules. The substance of the threads 

 'the'nucieus has been distinguished as LININ (I), that of the 

 by prato- granules as CHROMATIN (c/t). One or more larger 

 bodies, the NUCLEOLI (n), occur at the intersections 

 of some of the linin threads ; these, although deeply 



stained, do not take the same tint as the chromatin granules. 



The network of the nucleus lies within the nuclear cavity, which is 



t:. CO. Cell from 

 st.-uuinal hair of Tr 

 intia virginicu, 



,,ias.,.ic strands, (x 



