70 SCLEKEIDES 



eaiice of the groups or ' ' nests ' ' of brachysclereides in fleshy fruits 

 is less evident. It has been suggested that phylogenetieally they 

 may represent the remains of a former continuous shell of stone 

 cells. 



II. Material for the Study of Sclereides. — 



1. Bruchysdereides or "stone-cells" in the fruit and fruit 

 stalk of Ptjrus. Obtain a small fragment of the fruit of pear and 

 mount it in water under a cover glass. Imbedded in the thin- 

 walled parenchymatous tissue will be found small groups or 

 "nests" of stone-cells which appear yellowish-brown in color. 

 Examining one of these groups of stone-cells under high magnifi- 

 cation note the form of tlie cells, their greatly thickened walls 

 and the characteristic ramiform piis. After this preliminary 

 examination, remove the cover-glass, add several large drops of 

 a saturated solution of pliloroglucinol ^ followed by a drop or two 

 of hydrochloric acid. Note the brilliant red color assumed by the 

 walls of the sclereides. Often this color change, which occurs 

 when lignin is present in the walls, aids in the study of the 

 branching and the relationship of the ramiform pits. Study 

 carefully the form of the pits in both sectional as well as face 



view. 



Secure a trans-section of the fruit stalk of Pyrus and treat 

 it with phloroglucinol and hydrochloric acid as described above. 

 Add a cover slip and examine the sectiou under both high and 

 low magnification. The edge of the section is formed of several 

 layers of cork the innermost cells of which are in contact with 

 the phcllogen or cork cambium. Internal to the phellogen occurs 

 the cortex which is composed of thick-walled parenchyma tissue 

 in which are imbedded nests of stone-cells. Progressing inwards, 

 there next occurs a "ring" of fihrovascular hundUs. Each of 

 these bundles consists of an external ca]) of phcrs (which are 

 usually less brilliantly stained than the stone-cells of the cortex), 

 a strand of phloem, and a strand of xylem. The pith of the fruit 

 stalk is composed of botli i);irone]iyma as well as groups of stone 



cells. 



2. Astrosclerridrs. Obtain a pi-eiiaration of nuicerated "husk" 

 of the fruit of (Uirya or Juylans and examine it under low mag- 



1 Of. Appendix, p. 141. 



