4'2 THE VEGETABLE CELL IN GENERAL. 



exterior a delicate film. Meyer believes that the coloring matter 

 takes the form of grains of extreme minuteness which are inter- 

 spersed through the whole substance, while Tschirch holds that 

 the pigment, dissolved in a liquid similar to the ethereal oils, is 

 diffused through the mass. 



171. If starch is present in large amount in chloroplastids, 

 iodine causes at once a deep bluish-brown color ; but if the starch 

 is not very abundant, the characteristic blue reaction is concealed 

 by the yellow produced by the protein reaction of the protoplasm. 

 Hence it is well, after having removed the chlorophyll pigment 

 by alcohol and subsequent washing with water, to treat the speci- 

 men with moderatel}' strong potassic hydrate in order to dissolve 

 the protein matters. If this has been well done, and the speci- 

 men carefully freed from the potash, the protoplasmic mass and 

 its imbedded granules will seem to have complete!}- disappeared ; 

 but the skilful use of oblique illumination will show that an un- 

 dissolved trace of something having the former contours remains 

 behind. Application of iodine brings out minute blue j>oints 

 where the granules were. 



Chloral hydrate of the strength recommended in 53 may 

 replace potassic hydrate in this examination. 



172. The starch in chlorophyll granules is sometimes wholly 

 within the grannie ; but it is occa- 

 sionally especially in the case of 

 flattened granules found on their 

 exterior, forming a noticeable pro- 

 tuberance. 



173. When a plant containing 

 8 chlorophyll granules is kept for a 



time in darkness, the production of 



starch is arrested ; and if other forms of activity continue, even 

 that starch which has already accumulated in the granules soon 

 disappears. Furthermore, the 

 color of the granules is changed 

 from green to yellow ; and if the 

 change is not arrested at this 

 point by bringing the plant 

 again into the light, all the 

 granules will break up and be- 

 come apparently merged in the 



^ Fron, the cortex of 



