STRUCTURE OF THE CELL. 25 



2. The Endoplasm, the more internal, deeply stained proto- 

 plasm ; note that the staining is confined to fibrillse which form a 

 sort of network in the endoplasra, and to numerous minute 

 particles, the Microsomata. 



Observe in the. nucleus 



1. Stained fibrillae forming apparently a reticulum (ehromatin). 



2. The unstained matrix (achromatin) in which the fibrillaj 

 are imbedded. 



3. Cell-division. 



In order to study the process thoroughly the hairs on the stamens 

 of Tradescantia may be taken. A stamen is to be removed from 

 a bud, on a warm day, and is to be placed at once in a drop of 

 1 per cent, sugar- solution on a cover-slip ; the cover-slip is then 

 to be placed over a moist chamber as previously described. A 

 magnifying power of about 500 diameters is to be used. 



A terminal cell of one of the hairs, with a large and conspicuous 

 nucleus, is to be observed. It will be seen that the nucleus 

 gradually elongates in the direction of the longer axis of the cell ; 

 it becomes more granular, and the protoplasm of the cell aggre- 

 gates at its poles ; then the nucleus presents a striated appearance, 

 the fibrillse gradually arrange themselves parallel to the longer 

 axis of the nucleus, and approach each other at the poles ; thus a 

 characteristic nuclear spindle is produced ; the fibres are then 

 ruptured in the equatorial plane, and gradually collect at each 

 pole, so that two new nuclei are found. A layer of granular 

 protoplasm (the cell-plate) consisting of microsomata, is now 

 found in the equatorial plane, and it extends on each side until it 

 reaches the wall of the cell ; this layer becomes converted into 

 cellulose, and constitutes the dividing wall between the two cells. 



Good preparations of nuclei may be obtained by making longi- 

 tudinal sections of growing points (e.g. of the young roots of 

 }* and staining with heematoxylin. 



4. Structure of Chlorophyll-corpuscles and of 



Leukop last ids. 



a. Chlorophyll -corpuscles, or chloroplastids. Mount 

 a thin leaf of a Moss (e.g. Funaria), or the prothallus of 

 a Fern, in water ; note the corpuscles in the cells. 



