686 JOUKNAL OF THE KOYAL HORTICULTURAL SOCIETY. 



Apples, they hang vertically, the fruit is perfectly symmetrical in shape. 

 But if the stalk stand obliquely from the branch, as the Pear increases in 

 weight, it tends to break away at the insertion of the stalk in the Pear, as 

 ■can be easily seen from the adjoined figure of a Dr. Jules Guyot Pear : — 



Fig. 301. — Dr. Jules Guyot Pear, showing distribution 

 of forces to account for want of symmetry at point 

 of attachment to stalks. 



To resist this strain (that is, the resultant of the iceigJit of the Pear 

 and the tension along the stalk), a hump grows out at the base of the Pear 

 on the side away from the tree, thus preventing rupture at this point. 



Cells and Vessels. — It is not only in conspicuous organs, or even in the 

 <listribution of fibro-vascular bundles in leaves, petioles and stems, where 

 strengthening structures are developed, to bear weights or resist strains. 



a b c d e 



Fig. 302. — Vessels showing strengthening bands: a, pitted; 6, scalariform ; 

 c, ringed ; d, spiral ; e, reticulated. 



l)ut abundant illustrations might be taken from the microscopic tissues of 

 plants. 



Cells and vessels are frequently strengthened in various ways (fig. 302). 

 Thus the first-formed vessels of a stem have a spiral fibre running up the 

 inner side ; hence {d) they are called "spiral vessels"; sometimes the 

 ■strengthening is deposited in rings (c) ; occasionally both these kinds of 



