SCIENCE-GOSSIP. 



185 



CHARACTERISTIC BRANCHING OF BRITISH FOREST-TREES. 



By the Rev. W. H. Purchas. 

 {CoiiHntied from page 151.) 



The Oak {Quei'cus rohur, Linn.). 



IT has been thought by some botanists as well 

 as by foresters that we have in Britain two 

 distinct species of oak, i.e. the common or peduncled 

 oak {Qucrcus pedunculata, of Ehrhart), and the sessile- 

 fruited oak (0. sessiliflora, of Salisbury), to which 

 others have been inclined to add, as a third species, 

 or at least as a variety of Q. sessiliflora, the Q. 

 intermedia of Don. The botanical distinctions 



elude that the British oaks constitute but a single 

 species. In the majority of cases, however, a 

 difference in the mode of branching, which shall 

 presently be described, comes in to aid in the dis- 

 crimination, and is often sufficient to enable us to 

 recognise the sessile - fruited oak even in winter. 

 Selby well remarks of this tree that, " The growth 

 of the spray or branching is freer and less tortuous 

 than in Q. pedunculata, that the leaf-buds are larger. 



Qucrcus pedunculata. (Early summer state.) 



between these are found in the comparative length 

 of the fruit-stalk or peduncle, which varies from 

 almost nothing in some examples of Q. sessiliflora to 

 a length of two, or even three, inches and more in 

 Q. pedunculata, and also in the outline of the leaves, 

 to which may be added a difference in the form of 

 the winter buds and in the texture of their scales. 



In the case of the individuals which show these 

 differences at their maximum, it is not difficult to 

 decide to which of the supposed species each indi- 

 vidual should be referred ; but the inconstancy of 

 the characters and the existence of intermediate 

 forms have led most modern observers to con- 



and the bark in general much whiter in colour ; the 

 leaves also, when expanded, are usually larger, and 

 from the length of their petioles hang more loosely 

 and present a less tufted appearance than they do 

 in Q. pedunculata.'" (Selby, p. 248.) 



Arrangement of Leaves. — The leaves, and the 

 branches which arise from their axillary buds, are 

 arranged much more uniformly around the stem 

 than in the elm and beech, for in the oak the cycle 

 consists of five leaves, every sixth leaf beginning a 

 fresh series. It is found, however, that a line drawn 

 from leaf to leaf will pass twice round the stem or 

 shoot before the sixth leaf is reached. The diver- 



