] 6 THK PLANT CELL. 



ectoplasm forming a very delicate firmer layer next the cell-wall, 

 which certainly moves slowly, but not so fast as the more fluid 

 endoplasm. It is, however, hardly possible to distinguish opti- 

 cally between ectoplasm and endoplasm in the living cells of 

 T'allisneria leaf ; but in root-hairs these two portions may be made 

 out as distinct from one another, when the protoplasm is observed 

 under a high power. 



The chloroplasts are most convenientlj^ examined in the 

 smaller cubical cells near the edge of the leaf. Each chloroplast 

 is ellipsoidal in shape, small when compared with the nucleus, 

 and of a light greenish-yellow colour, the latter being due to the 

 presence of chlorophyll, a pigment which permeates the substance 

 of the chloroplast ; the ground-substance of each chloroplast is, 

 however, protoplasmic in nature. 



The eff"ect of certain simple reagents upon the living cell must 

 next be studied ; and for this purpose it is usual to employ : — 



(a) A solution of acetiC aCid in water, 20 per cent, strength. 



(b) A solution of iodine in a dilute solution of potassium iodide, until 

 the whole is of a dark sherry-red colour. 



(c) Sehulze'S solution. This is a solution of iodine and potassium 

 iodide in chloride of zinc solution. * 



(d) Iodine solution, followed by a drop of concentrated SUlphUPie 



acid. 



The reaction of the cell and its parts to these reagents will 

 now be described. 



(a) Acetic acid, 20 per cent, solution in water, will, if added 

 (one drop under the cover-slip of the preparation) to the water 

 in which the portion of Vallisneria leaf is mounted, produce the 

 following effects : — 



i. The protoplasm shrinks away from the walls of the cell observed, 

 and retracts towards the middle of the cell-cavity, strands or " bpidles " 

 of protoplasm being observed which at first connect the main mass with 

 the cell-wall. 



ii. The whole cell will shrink somewhat, the walls becoming convex 

 inwards. 



iii. The nucleus takes on after a short time a punctate appearance, 

 probably due to coagulation of certain substances in its interior. 



The retraction of the protoplasm is known as " plasmolysis,'' 

 and is dependent upon the disturbance of the osmotic equilibrium 



* The exact quantities are as follows : — 0'2 grm. iodine added to » 

 solution of 70 c.c. cone, zinc chloride and 10 grms. of potassium iodide. 



