44 THE VEGETABLE CELL IN GENERAL. 



tage in thin sections of many starchy tissues, by the use of dilute 

 tincture of iodine, which colors them more or less deeply yellow. 

 Millon's reagent colors them red. 



Owing to the minuteness of the leucoplastids, the following 

 explicit directions by Strasburger will aid in their detection : 

 Make thin longitudinal sections through the upper part of a 

 young pseudobulb of Phajus grandifolius, taking care that the 

 cut extends to its green surface. Immediately place the sections 

 in an alcoholic solution of iodine diluted with one half its volume 

 of water. (Picric acid may be advantageously used instead of 

 the iodine solution.) Jn good preparations the leucoplastids will 

 be seen in the inner part of the section as small staff-shaped 

 bodies which, at the first glance, appear to be homogeneous, but 

 are afterwards recognized as somewhat granular in structure. 

 The section is next to be examined nearer its outer part, and it 

 will then be seen that the bodies there possess a green color, 

 are larger, and lenticular in form. They are also plainly porous, 

 their increase in size being apparently associated with a spongi- 

 ness of their substance. Their size diminishes towards the outer 

 cellular la}'ers, the}' become somewhat rounded, and finally take 

 the familiar form of chlorophyll granules. Prismatic colorless 

 protein crystals are frequently associated with these bodies. 

 In sections which are placed in water, the leucoplastids disap- 

 pear almost instantaneously, and even the chlorophyll granules 

 soon begin to disorganize, while the swollen protein crystals then 

 appear as colorless parts of the latter. 



In the rhizome of Iris Germanica the sections for examination 

 must be taken parallel to the surface. In uninjured cells the 

 leucoplastids appear as collections of protoplasm at the end of 

 each starch-granule. If the section is in water, the leucoplastids 

 become granular and finally break up into minute granules which 

 show the Brownian or molecular movement. 1 



Chromoplastids, or the color-granules which occur abundantly 

 in flowers and fruits, will be specially treated later. 



175. Protein granules. The protein matters in plants have 

 been divided into two classes: (1) the active, such as active 

 protoplasm, the nucleus, etc. ; (2) the reserve, which can change 

 their dormant condition and become active when occasion de- 

 mands. Inactive, amorphous protoplasm, as it sometimes exists 

 in certain cells, where it is simply a tough shapeless mass, does 

 not need further consideration at present ; the reserve matters 



1 Strasburger: Da.s botan. Practicvnn, 1884, pp. 67, 68. 



