SECT. I 



MORPHOLOGY 



59 



The stimulus caused by wounding the tissues in making the prepara- 

 tion frequently increases the activity of the movement (^^) ; apparently 

 it quickens the transport of nutrient material toward the wound. 



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

 afforded by the staniiual hairs of T radescantia vinjinica. In each cell (Fig. 59) 

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

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

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

 may thus alter the position of the cell nucleus. 



When the protoplasm is in rotation, the cell nucleus and 1(1 / 



chromatophores are usually carried along by the current, but \<vj| ,[_ .f 



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, especi- 

 ally in the genus Nitella, aflord 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 de- 

 velopmental stages this structure appears to be 

 traversed by special filaments, which can be demon- 

 strated by suitable staining (Fig. 56) (^''). 



The portion of the cytoplasm which forms the network or 

 honeycomb appears to be specially concerned with the nutri- 

 tive processes, while the fibrillar plasma influences the process 

 of development ; they are respectively termed trophoplasm 

 and kinoplasm ; the latter has also been called archiplasm. 

 When traced to their origins the limiting layer of the cyto- 

 plast is found to belong to the kinoplasm, the walls of vacuoles 

 to the trophoplasm. Albuminous substances, precipitated 

 by the fixing agent, have not infrequently been mistaken for 

 structural features of the cytoplasm (^'). 



1 



;; 



'■n 



/-'-i. 



Fig 



9. — Cell from a 

 staminal hair of Tra- 

 desca ntia virgin lea, 

 showing tht; nucleus 

 suspended by proto- 

 plasniic strands, (x 

 240.) 



The Cell Nucleus (^*). — The resting nucleus has 

 a reticulate or honeycomb structure forming an 

 anastomosing network (Fig. 56), which, however, in living objects can 

 only be distinguished by the finely dotted 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 deter- 

 mine 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 has been distinguished as LININ 

 (/), that of the granules as chromatin (cJi). 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 



