DIV. I 



MORPHOLOGY 



17 



- n 



cytoplasm of each of the cells of the common filamentous fresh -water 

 Alga Cladaphora glomerata (Fig. 7). 



The living nucleus has a finely dotted appearance. It usually 

 contains one or several larger, round, highly refractive granules or 

 droplets, the use of which is unknown but which are called NUCLEOLI 

 (Fig. 2 n). The nucleus, the consistence of 

 which appears to be that of a tenacious fluid, 

 is surrounded by a NUCLEAR MEMBRANE 

 (Fig. 2 kw) by which the surrounding cyto- 

 plasm is separated from the NUCLEAR CAVITY. 



Some insight into the finer structure of 

 the nucleus is obtained from properly fixed 

 and stained preparations. In these a deeply 

 staining reticulum of CHROMATIN, which 

 appears to consist mainly of proteids con- 

 taining phosphorus, is evident. The nucleoli 

 are situated in the meshes of the network 

 within the nuclear cavity which is filled with 

 the NUCLEAR SAP. The nucleoli stain deeply 

 but differently from the chromatin. 



In many nuclei the reticulum appears to be formed 

 of a substance called LIXIN that stains feebly, and 

 the chromatin to be embedded in this as minute 

 granules. In some Algae and Fungi the nucleoli 

 contain a proportion of the chromatin. They are 

 thus not strictly equivalent to the nucleoli of the 

 higher plants, as is further shown by their behaviour 

 in the process of nuclear division ( 13 ). 



It is still unknown what part the nucleus 

 takes in the vital phenomena of the proto- 

 plast. It is, however, clear that it is neces- 

 sary for the maintenance of life in nucleated 

 cells. It also appears to be of great import- 



ance as the main bearer of the hereditary FIG. 7. A ceil of 



characters glomerate, fixed with 1 per cent 



3. The Chromatophores().-In the "" 

 embryonic cells of the embryo and of growing After STRASBURGER.) 

 points, where the chromatophores (Fig. 2 ch) 



are principally located around the nucleus, they first appear as small, 

 colourless, highly refractive bodies of circular, spindle-shaped or fila- 

 mentous form. In older cells they attain a further development, as 

 CHLOROPLASTS, LEUCOPLASTS, or CHROMOPLASTS. Since these bodies 

 have the same origin they are all termed CHROMATOPHORES. 



(a) Chloroplasts. In parts of plants which are exposed to the light 

 the chromatophores usually develop into chlorophyll bodies or chloro- 

 plasts. These are generally green granules of a somewhat flattened 



C 



