78 THE TREE BOOK 



lowed to escape. In spring, the lentioles are 

 opened again by the pressure of new cork cells 

 forming beneath them. 



The seeds of many trees do not "come true 

 to type," that is the trees which they produce 

 are not like the parent stock. The oaks, un- 

 like most of their neighbors, are often cross- 

 fertilized by the wind, that is, the pollen from 

 one kind of oak is blown on to the pistil of an- 

 other and germinates there. The seedling 

 which this union produces is a hybrid, with 

 characteristics of its parents, but unlike either 

 one. We may find many of these hybrid oaks 

 even in a short walk through the forest. An 

 English nurseryman, experimenting with the 

 hawthorn, pr^^^d twenty-nine distinct va- 

 rieties from^j^^vAnother investigator found 

 that not on^^P^ 20,000 of the weeping-ash 

 came true to type. There are many trees of a 

 weeping habit. People used to think that such 

 trees were produced by planting a seedling with 

 its roots ia the air and its head in the ground ! 

 Others a little better informed in tree science, 

 thought that they were produced by grafting 

 in buds set upside down. As a matter of fact, 

 these trees are fashioned by grafting scions of 

 the species desired upon an upright tree of a 

 closely related variety. Scions are pieces of 



