STEM. SIEVE-TUBES. 85 



(iii.) Gambiform cells. 



Treat some sections with Schulze's solution ; all the 

 walls of the soft bast turn blue (cellulose), but the 

 sieve-plates appear yellow or brown, (cf. longitudinal 

 sections.) 



II. Cut longitudinal sections through the soft bast : 

 either radial or tangential sections will do. Mount 

 some in iodine solution. The transverse sieve-plates 

 will be brought into prominence by the deep yellowish 

 brown staining of the mass of substance, which 

 surrounds them : this may consist of 



a. A Callus mass, which immediately surrounds 

 the plate, and is apparently a derivative of cellulose, 

 thpugh it differs from it in its properties : the size of 

 the callus mass is variable according to season, age, 

 &c., being greater in autumn, and in old sieve-tubes. 



b. Protoplasm, which is usually collected in close 

 contact with the sieve-plate (or callus if present), and 

 more especially on its upper side. 



Note, i. the oblong form of the segment of 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 have stained 

 deeply. 



III. Mount some sections in water, and having found 

 a sieve-plate with callus, run some dilute potash under 

 the cover slip. 



