124 THE STRUCTURE OF FLOWERS. 



sjmmetricallj round tlie insertion of tlie stalk as an orange ; 

 but if the pedicel projects obliquely from the branch, they 

 then thicken along the upper side, forming a sort of buttress 

 running down into the stalk, which also itself tends to 

 thicken. This enlargement, which gives the peculiar " lop- 

 sidedness " to several kinds of pears especially, and in a 

 lesser degree to some sorts of apples, is simply due to the 

 fact that the force required to counteract the resultant of 

 the two forces, gravity and tension — which act vertically 

 downwards and along the stalk, respectively — must be 

 increased in proportion as the direction of the stalk ap- 

 proaches the horizontal one. The accompanying diagram 

 (Fig. 38) represents the basal end of a Dr. Jules Guyot pear 

 ^ and in the position in which it hangs 

 upon the tree. The lettev lu (weight) 

 is in the line of gravity, t (tension) 

 acts along the stalk, while r coun- 

 teracts the resultant, which tends to 

 tear the pear from the stalk at the 

 upper side. This strain must be 

 met, and the increased thickness 

 Fig. 38.— Diagram of the end of a along this Upper sidc enables the pear 



Dr. Jules Guyot pear. , • j_ •. j -i • •^ 



to resist it, and thus prevents the 

 frait, especially if it be a large and heavy kind, from being 

 wrenched from the stalk. 



A somewhat similar development often occurs with plums 

 and lemons ; only, as there is no receptacular tube in either 

 case, the weight of the fruit causes them to produce a thick 

 fold in the carpel on the under side, together with some 

 degree of hypertrophy on the upper, where the tension occurs. 



It is not uninteresting to notice how branches of trees 

 similarly sustain the strain produced by their own weight. 

 This is done by growing at an acute angle (originally caused 



