80 PEACTICAL BOTANY. 



4. Masses of Xylem-fibres, wlricli appear as before. 



VIII. Cut tangential sections of the phloem of a 

 similar stem : treat as before, and observe 



1. The form and arrangement of the medullary 

 rays as in the xylem, but the walls of the cells are 

 thinner, and not lignified : copious protoplasm is to be 

 found. 



2. Phloem-parenchyma, the cells of which differ 

 in their cell-contents 



(a). Some containing crystals. 



(&). Others with copious protoplasmic contents. 



Both forms will be seen to have been derived by 

 division from original elongated cells with pointed ends, 

 since they are arranged in groups of this form. 

 (cf. cambium.) 



3. Sieve-tubes answering to the description given 

 for radial sections (cf. Cucurbita). The sieves are oblique, 

 the form of the successive segments oblong. The sieves 

 are callous, and are easily recognised in sections stained 

 with iodine or eosin. 



4. Bast-fibres as before in radial sections. 



IX. Cut tangential sections through the cambium 

 of the stem of Elm : treat with dilute potash, and mount 

 in glycerine. Examine first with a low power, and note 

 that the general arrangement is similar to that already 

 seen in tangential sections through the mature tissues, 

 also that the form of the cells, in each part of the 

 cambium-zone, is like or similar to the average form of 

 the elements of the mature portion of wood or bast, 

 which borders on it in a radial direction. Thus the 

 cambium is differentiated into 



1. Cambium of medullary rays, which appears as 



