











2K5 



DR. M. T. MASTERS ON THE MORPHOLOGY*, 



leaves 



occur. 



But if the distiuctiou between growth and 







development be kept in mind, it would seem that the concres- 

 cence is an indication of arrested and irregular development 

 associated with disproportionate rapidity of growth. In the 

 free leaves the balance between growth and development is 

 preserved, the base of the leaf is symmetrical and the parts are 

 all in regular proportion. It is worthy of incidental mention, 

 with reference to the possible genealogy of Conifers, that some 

 species of Lycopodium, as L. annotinum, and Charnrecyparis have 











concrescent leaves and projecting pulvini. 



In some cases all or a large proportion of the adult leaves are 

 concrescent, as in Cupressus nutkaensis, Callitris, Frenela, &c. 

 In other instances the concrescence is much more apparent in 

 the lateral than in the median leaves, e.g. in Libocedrus chilensis, 

 L. austrocaledonicus, Cupressus Lawsoniana, many Retinosporas, 

 Ac, where the branch system is flattened, and where, as already 

 mentioned, the leaves are regularly arranged in decussate pairs. 

 Here there appears to be a relative excess or greater rapidity of 

 growth in the lateral pairs of leaves, alternating regularly with a 

 diminished intensity of growth in the median pairs of leaves. 

 In many of these cases, where the leaves are in decussate pairs 

 the free tips of the lateral leaves are in close proximity to the 

 corresponding tips of the median leaves. This proximity is 

 misleading ; thus, in Thuya gig ant ea^ Libocedrus decurrens, or any 

 similar plant, if we fix upon a median leaf, or a pair of median 

 leaves, as a starting point, it will be found on examination that 

 the leaves next in order of time or origin to those from which we 

 start are not those which are nearest, but those which are removed 

 to some distance by the uplifting process, and conversely that 

 the pairs of leaves nearest to those taken as the starting point 

 are further removed in sequence of production. In other words, 

 the closest fellowship is between any given pair of leaves and the 

 lateral pair above them, not between those which happen to be 

 almost on a line with them. On the long fast-growing leader or 

 extension shoots the degree of concrescence and the rapidity of 

 growth are more nearly equal in the lateral and in the median 

 leaves. 

















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Secondary Leaves of Pinus. 



The " needles " of Pinus, like those of Sciadopitys (which will 

 be treated of in another section), have been considered by some 



































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