



8 



starch-bearing; this fact benig indicated by the darkness in im- 

 itation of the color produced in this part of the section by a 

 sohition of iodine. At b and c are the scars of the last two 

 leaves of the previous season, and from them pass inward and 

 downward the vascular tissue that gives elasticity and strength 

 to the twicf. Other similar but smaller vascular threads are 

 seen above, receding from the bases of the bud-scales, and 

 uniting into a cylinder of woody tissue, still in a formative 

 condition. The remaining part of the bud consists of small, 

 many-sided cells packed together, a large number of them 

 bearing complex, sphere-shaped crystals of oxalate of lime, 

 while others are filled with semi-solid substances composing 



bH 



I' 



f 



I' 



I 



-I 



I 



an impure form of protoplasm. The feature of most interest 

 in this connection is the sharp line separating the starch-bear- 

 ing cells of the pith from those in the younger pith just above, 



■ J 



in the contents of which starch is entirely absent. There is f 



a definite localization of the starch, as a rule, in or near all 

 terminal buds that are fully matured. In those gathered be- 

 fore the processes of growth are completed, the starch maybe 

 scattered in all parts of the soft tissue, and especially in that 

 portion lying between the zone of wood and the rind. 



Besides the presence of starch, there is another marked 

 difference between the pith indicated by the shading and the 

 younger portion above, containing the albuminoids and crys- 

 tals. The latter, it has been said above, is composed of thin- 

 walled cells, and not materially different from those in all 

 other parts of the bud. But the starch-bearing cells have 

 their walls much thickened, and in such a manner that canals 

 are left extending from the original cell wall to-the free inte- 

 rior. These canals of adjoining cells meet at the juxtaposed 

 w^alls, so that provision is thus made for the ready transfer of 

 material from one part of the storage tissue to any other. In 

 figure 2 is shown a portion of the tip of the starch-bearing pith 

 in the terminal bud of a Duchess pear, and* the adjoining thin- 

 walled pith. At this line, which is usually somewhat convex, 

 the tissue w^'ll often give way in making the sections, leaving 

 the firm, thick-walled pith tvith a ragged edge, A few of the 

 starch-bearing cells, highly magnified to show the details of 



their canaliculate structurCj are shown in figure 3 



