48 Botanical Microtechnique 



the tissues from the paraffin or crumbling within the tissues. If there 

 is abundant ribbon and if seriation need not be maintained, melt 

 a piece of ribbon on a dry, used slide, and examine cjuickly with a 

 microscope. A magnification of 400 can be used. It is possible to see 

 the chromosomes at metaphase and even at early prophase in onion 

 root-tip cells. The position of chloroplasts in cells can be observed; 

 the degree of granularity of cytoplasm, vacuolation, and plasmolysis 

 can be estimated. The success of the processing can therefore be 



"X 



^ 

 "^ 



"^ 

 ^ 

 "^ 



B 



Fk;. 6.1— Paraflii) ril)l)()ii: .1. straiglit ribbon. noKhcd if desired by trimming one 



edge ol the paiaiiin i^loek as in Fig. 15.1L; B, curved ribbon; C, trimming of 



paiailin l)i<)(k along doited line to correct curxalure. 



judged at this stage in accordance with the criteria discussed in 

 Chap. 11. 



The optinnim tliickness of section h)r any specific sid)ject can 

 be ascertained at this point. An ex})erienced worker can make a good 

 guess, subject to verification, by examining the ribbon. Study Fig. 

 6.5 A, a perspective sketch ol a portion of a leaf with both layers of 

 epidermis omitted. Assume that sections have been ciU 20 n in 

 thickness. Note in li that a section of this thickness woidd encomj)ass 

 two or three la)ers of narrow columnar palisade cells, and consider- 



