1 90 BOl'ANICAL MICROTECHNIQUE. 



II. The Resting Nucleus and its Constituents. 



a. Recognition of the Resting Nucleus. 



331. If one is concerned simply with the recognition of 

 resting nuclei in an organ or a tissue system, this should no 

 longer present serious difficulties in the Phanerogams, the 

 Pteridophytes, or the Mosses. Especially by fixing with 

 chrom-osmic-acetic acid ( 309) or with chromic-acid-plati- 

 num-chloride ( 312), and staining according to one of the 

 methods described in 320 to 325, this object may always 

 be realized certainly and without great trouble. By stain- 

 ing in mass with haematoxylin ( 314) I have also always ob- 

 tained very sharp nuclear staining at a little distance from 

 the surface. Very instructive preparations may also be usu- 

 ally obtained from algae and fungi by the use of the same 

 methods. For most algae \% chromic acid ( 305) is an ex- 

 cellent fixing medium, and good stainings may also be ob- 

 tained by the picro-nigrosin method ( 329). 



332. To stain the nucleus in the starch-filled oospheres of 

 Nitella, Overtoil (II, 35) used a mixture of potassium f err o- 

 cyanide and hydrochloric acid, diluted with 8 10 times its 

 bulk of water. The starch was then converted into sugar 

 by the hydrochloric acid and, at the same time, the Berlin 

 blue produced by the decomposition of the ferrocyanide 

 stained the nucleus. This author recommends chloral hy- 

 drate for clearing. 



333. Special difficulties are sometimes due to the cuticu- 

 larized or slightly pervious membranes which often invest 

 reproductive organs. In such cases the subsequent staining 

 of microtome sections will give the best results. 



334. If one wishes, in especially difficult cases, as in fol- 

 lowing the development of spermatozoids, to obtain a very 

 sharp differentiation of nucleus and cytoplasm, double stain- 

 ing may be used with good results. Guignard (I) used for 

 this purpose, with material fixed with osmic acid or with 

 alcohol, the staining method with fuchsin and methyl green 

 described in 326. 



