SUGGESTED UKAWINCS AND AOTES 71 



iiifieatioii. The two most abundant cell ty})e8 are (1) parenchyma 

 cells which vary from nearly isodiametric elements to irregular 

 forms, and (2) astrosclereides which exhibit remarkable varia- 

 tion in the form and proportion of the "arms." The thick 

 stratified wall and branched pits show very clearly in these 

 sclereides. It is instructive to note the frequent similarity be- 

 tween certain of the parenchyma cells and the sclereides, indicat- 

 ing the origin of the latter from parenchyma by the process of 

 secondary sclerosis w^hich has been described in the Introduction 

 of this exercise. 



For comparative purposes, examine trans-sections of the 

 petiole of the leaf of Camellia after staining them in phloroglu- 

 cinol and hydrochloric acid. Study the sections under high 

 magnification and note the elaborately branched areas of astro- 

 sclereides. Sections through the lamina of the leaf should also 

 be stained and examined for the huge branched sclereides which 

 occur in the midst of the mesophyll. 



3. Macrosclereides. Obtained a small amount of macerated 

 bean testa and examine it under low magnification noting the 

 small, tightly packed groups of columnar macrosclereides. Note 

 that the lumen of each macrosclereide is widest near the base of 

 the cell, being reduced to a narrow% virtually occluded channel 

 above. For illustrations of macrosclereides in situ in the testa 

 of seeds of the Leguminosae refer to Eames and MacDaniels (p. 

 294, Fig. 134c), Hay ward (p. 342, Fig. 174), and Netolitzky 

 (1926, p. 159). 



III. Suggested Drawings and Notes. 



1. Prepare drawings to show the form and pit relationships 

 of a small group of stone-cells in the fruit of the pear. How may 

 the fact be explained that some of the ramiform pits or their 

 branches fail to terminate at the "edge" of a stone-cell at a given 

 level of focus? 



2. Make a diagrammatic drawing of the trans-section of the 

 fruit stalk of the pear, showdng and labeling all the important 

 tissues and regions. Summarize, in the form of notes, the posi- 

 tions and mechanical significance of the stone-cells and fibers in 

 this organ. 



