SIEVE-TUBES 115 



Note, I. the oblong form of the segments composing 



the sieve-tubes. 



ii. The companion-cells, short with granu- 

 lar protoplasm, and nucleus, 

 iii. Cambiform cells of similar form to the 



segments of the sieve-tubes. 



Other sections should be stained with eosin, then 

 washed, and mounted in glycerine. The sieve-tubes 

 will be readily seen, as their contents will be stained 

 deeply. 



III. (a) Mount some sections in water, and having found a 

 sieve-plate with callus, run some dilute potash under the cover- 

 slip. The callus-mass swells ; the protoplasm also swells : the 

 section thus becomes more transparent, and the cellulose basis 

 or true sieve becomes more apparent, and its pores can be easily 

 seen. 



(&) Treat another section in which a callus has been found with 

 Eussow's callus -reagent (see Appendix A) : the callus stains a 

 deep brown. 



(c) Treat another preparation with corallin-soda (see Appen- 

 dix A), and mount in glycerine : the callus stains pink. 



(d) Stain another preparation with Hoffmann's blue in 50 

 per cent, alcohol for 24 hours, wash with water, and mount in 

 glycerine : the callus is stained deeply. 



IV. Treat some fresh sections with iodine, then dry 

 off the superfluous fluid with blotting-paper, and 

 mount in a single drop of strong sulphuric acid. The 

 cellulose walls and callus will swell; the protoplasm 

 will contract. Look carefully over the protoplasmic 

 contents of the sieve-tubes for the points where sieve- 

 plates have been ; ,here it will be found that fine strings 

 of protoplasm, which passed through the sieve-plate, 

 connect the protoplasmic masses on opposite sides of ihe 



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