MATERIAIv FOR STUDY OF PARENCHYMA 59 



''unspecialized" nature. ])ut it is evident that many factors, 

 hereditary as well as environmental, influence the process of "re- 

 gressive differentiation" in parenchyma and that our knowledge 

 of the "potentialities" of such tissue is still in an exploratory 

 stage. 



II. Material for the Study of Parenchyma.— At this point 

 suggested material for a preliminary study of storage and photo- 

 synthetic parenchyma is described. Additional examples of 

 parenchyma are given in several of the later exercises in this book. 



1. Storage parenchyma. As noted above, parenchyma tissue 

 often serves as a region for storage of many different substances, 

 particularly starch. The cotyledons of bean embryos, during the 

 early stages of seed germination, provide useful material. 

 Examine thin sections as well as partially macerated tissue, not- 

 ing the closely-packed starch grains in the parenchyma cells. 

 Under high magnification, the type and distribution of the simple 

 pits on the various faces of the wall may be clearly studied. 

 Additional examples of storage parenchyma are furnished by the 

 cortical parenchyma of the young root (e.g., Ranunculus) and 

 the parenchyma tissue of the potato tuber (Solannm tuberosum). 



2. Photosynthetic parenchyma. In the subepidermal region 

 of young stems and in the mesophyll of leaves, the thin-walled 

 parenchyma cells contain chloroplasts and perform the function 

 of photosynthesis. Obtain a thin transverse section of the stem 

 of Begonia, and, after mounting it in water, examine the prepara- 

 tion at low magnification. Notice that the cortex (i.e., the region 

 between the epidermis and the cylinder of vascular bundles) and 

 the pith are composed of large, thin-walled "isodiametric" cells. 

 (Note: Several layers of small collenchyma cells are found at the 

 outer edge of the cortex and may be disregarded in this study.) 

 Under low magnification observe that large, solitary prismatic 

 crystals as well as druses occur in many of the parenchyma cells. 

 Frequently, the form of the crystals is highly irregular. Under 

 high magnification, the cytoplasm, vacuole and small chloroplasts 

 can be readily studied especially if the sections are mounted in 

 .1% solution of neutral red.^ Because of the large size of the 

 cells, the nucleus is only seen occasionally in trans-sections of the 



1 Cf . Appendix, p. 142, 



