THE CUCUMBER FAMILY. 147 



This movement enables the tendril to search for a 

 support. If the little hooked end catches a twig, the 

 tendril at once begins to coil round it, and at the same 

 time grows thicker, and coils up into a spiral. But it 

 will be noticed that it coils in opposite directions two 

 or three times, with straight pieces between the 

 opposite groups of coils. This prevents the tendril 

 from breaking under tension. It can be imitated by 

 fixing one end of a piece of string, pulling it tight, then, 

 by twisting the other end for some time and sub- 

 sequently relaxing it, the string will suddenly twist 

 upon itself the opposite way, till it comes to rest. You 

 have put force into it which, to be in equilibrium, must 

 be balanced by twisting in the contrary direction. The 

 tendril does a precisely similar thing. 



Of other genera, the reader will be familiar with 

 the Water-melon {Citrid'lus vulf/a'ris) and the Luf'/a, 

 which produces a dry and fibrous fruit, often used in 

 baths and for various other purposes. The Bottle-gourd 

 (Lageiia'ria vidga'ris) has a globular top with a con- 

 tracted base. This is due to the fact that the ovules in 

 the lower (stalk end) part were not fertilized; as the 

 result of fertilization is not only the development of 

 the embryos in the seeds, but the formation of the 

 fruit which contains them. 



Gourds and pumpkins belong to another genus 

 {Cucurhita). 



