ix THE HISTOLOGY OF THE SHOOT AND ROOT 105 



EXPT. 96. Transfer the thinnest section observed in Expt. 95 to 

 alcohol, and let it remain for twenty minutes to bleach it. Now stain 

 it with iodine solution, mount in glycerine, and examine a vascular 

 bundle under the high power. Note 



(i) The endodermis, a single layer of cells containing starch. The 

 starch grains stain blue. 



(ii) The pericycle, a layer of cells inside the endodmeris. 



-xy. 



Fi 



FIG. 131. Diagram of old stem of Sunflower as seen in transverse section, showing 

 an almost complete cylinder of secondary tissues, interrupted by medullary rays. 

 (x 6.) Ep, epidermis \ co, cortex; Scl, sclerenchyma patches; Ph, phloem; 

 cb, cambium ; jry, xylem ; Pi, pith. 





(iii) The phloem inside the pericycle ; the transverse walls of the sieve 

 tubes will be stained yellow, and the perforations through which the 

 strands of protoplasm pass may be stained brown. 



(iv) The cambium, several layers of cells inside the phloem. 



(v) The xylem between the cambium and pith. This can be easily 

 recognised by the large cavities of the vessels. 



(vi) The pith, which fills the interior of the stem. 



EXPT. 97. Select a very young stem of the Sunflower. This can 

 be obtained by germinating seeds, and planting out the young plants in 

 plant pots. The stem should not be more than th of an inch in 



