INTRODUCTION. 7 



until a severe frost followed by a thaw brings them 

 down. The buds, leaves, and flowers are all much at- 

 tacked by gall-forming insects, many different kinds 

 being found on one and the same tree. 



It is not until the oak is from sixty to a hundred 

 years old that good seeds are obtained from it. Oaks 

 will bear acorns earlier than this, but they are apt to be 

 barren. A curious fact is the tendency to produce large 

 numbers of acorns in a given favorable autumn, and 

 then to bear none, or very few, for three or four years 

 or even longer. The twisted, " gnarled " character of 

 old oaks is well known, and the remarkably crooked 

 branches are very conspicuous in advanced age and in 

 winter (Plate II). The bark is also very rugged in the 

 case of ancient trees, the natural inequalities due to fis- 

 sures, etc., being often supplemented by the formation 

 of " burrs." 



A not inconsiderable tendency to variation is shown 

 by the oak, and foresters distinguish two sub-species 

 and several varieties of what we regard (adopting the 

 opinion of English systematic botanists) as the single 

 species Quercus robur. 



Besides forms with less spreading crowns, the spe- 

 cies is frequently broken up into two Q. pedunculata, 

 with the female flowers in rather more lax spikes, and 

 the acorns on short stalks, the leaves sessile or nearly so, 

 and not hairy when young; and Q. sessiliflora, with 

 more crowded sessile female flowers, and leaves on short 

 petioles and apt to be hairy. Other minute characters 



