106 PRACTICAL BOTANY 



noted here also, similar to those above described as 

 occurring in the medullary rays of the wood. The 

 cells contain copious protoplasm. 



2. Phloem-parenchyma, the cells of which differ 

 in their cell contents 



a. Some contain crystals. 



b. Others have 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. 

 Compare the form of the cambium cell (IX.). 



3. Sieve-tubes answering to the description given 

 for radial sections. The sieves are oblique, the form of 

 the successive segments oblong. The sieves are callous 

 (see p. 115), and are easily recognized 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 or "eau 

 de javelle," and mount in glycerine. Examine first 

 with a low power, and note that the general arrange- 

 ment 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 to 

 consist of roundish cells, resembling cells of the 

 mature medullary rays in form. 



2. Cambium, from which all the other tissues are 

 derived, the cells of which have a prismatic form. 



