58 



VEGETABLE HISTOLOGY. 



A good way to get a longitudinal view of the cells is to strip 

 off the epidermis from a Lily petiole ; the collenchyma cells will 

 come off with it and may readily be studied in water or iodine 

 solution. 



In iodine solution the collenchyma cells are seen to contain 

 protoplasm and a nucleus. If the excess of iodine solution be 

 removed and sulphuric acid reagent be added, the cell-walls will 

 swell and assume a blue color, which shows that they are cellu- 

 lose in nature. Chlor-zinc-iodine solution gives the same result. 



While studying collenchyma in the petiole of Burdock atten- 

 tion should be given to the whole section, as another illustration 

 of the dicotyledonous type of stem structure. A number of dis- 

 tinct moccasin-like areas may be observed, arranged in a single 

 circle and separated from each other by plates of ordinary 

 parenchyma cells. These are the fibro-vascular bundles, con- 

 sisting of bast and wood fibres and tracheary vessels, just as in 



Fig. 37. Sketch of cross-section 

 of petiole of Burdock, a, 

 patch of collenchyma ; b, ring 

 of bundles ; c, pith with hole 

 in center. 



Fig. 38. Cross-section of collen- 

 chyma of Burdock magnified, 

 showing thickened angles of cell- 

 walls (Bastin). 



the Geranium stem. But as in the case of succulent plants in 

 general, so here the vascular bundles have not coalesced, so that 

 there is no continuous ring of bast fibres, cambium zone and 

 wood fibres and vessels, as is the case in the Geranium. Next 

 to the circle of bundles comes the pith, the center of which is 

 occupied by a cavity. Cork cells are absent. 



Let a cross-section of Burdock soak a few minutes in phloro- 

 glucin solution, then add hydrochloric acid and note that the 

 only lignified material occurs in the vascular bundles in the 

 fibres and vessels. 



