VI] DEVELOPMENT OF FORM 69 



flattened or depressed slightly rounded head results, re- 

 minding one somewhat of a mushroom on its stalk, or 

 even of an umbrella (Fig. 2). 



Such umbellate crowns are common in old Pines, e.g. 

 the Scots Pine, and are so characteristic of certain species 

 that they have been termed Umbrella Pines, e.g. Pinus 

 Pinea (Fig. 2). 



We thus see that every possible variety of form, start- 

 ing with the terete or columnar form, tapering upwards, 

 or rounded above and more or less regularly cylindroidal, 

 and ending with the widely spreading tabular or depressed 

 umbrella-like head, is attainable in trees with a single 

 main stem from which branches radiate regularly on all 

 sides, by the mere processes of stoppage of growth of the 

 leader, relative rapidity and continuance of growth of 

 upper and lower laterals, and cleaning of the bole by the 

 disappearance of the lowermost main branches as they die 

 off in order of age from below upwards. 



Of course the reader will at once see that the whole 

 process resolves itself into a sort of natural pruning, the 

 effects of which vary according to the disposition of the 

 buds and twigs concerned, and the agents of which are 

 those studied in Chapter IV. 



It now remains to be seen how the equally great 

 variety of similar forms result from such changes in trees 

 of which the branching is apparently at any rate less 

 regular and simple than in the cases cited. 



If we examine a young Apple, Plane or Oak, in 

 what nurserymen and foresters term the sapling stage, 

 it will usually be found to present the following features. 

 The main stem runs right through as a common axis, and 

 terminates above as a leader, pointing vertically and 

 keeping the prominence expressed in its name by growing 

 forwards and giving off twigs and branches in acropetal 



