



* 







2G4 DB. M. T. MA.STEBS OK THE MORPHOLOGY, 



Sometimes leaves of a primordial character occur even on the 

 fruiting-branches ; thus, in Juniperus conferta or J. taxifolia it is 

 common to see fruits borne on branches covered with linear 

 leaves, and I have latterly seen a bush of Betinospora squamosa 

 (a form of Thuya pis if era with primordial foliage only) covered 

 with cones. 





Concrescence or Inseparation. 



One of the most common causes of heteromorphy in the foliage 

 of Conifers arises from the so-called " adnation " or " decurrence" 

 of the leaves. These terms, however, as has been already 

 mentioned under the head of the Cotyledons, are misleading, 

 inasmuch as they imply a previous isolation and subseqnent 

 union. The apparent union is the result of a continued con- 

 nection between the base of the leaf and the branch from which 

 it springs, instead of a separation or detachment such as usually 

 takes place. It is, in reality, due to the arrest or non- occurrence 

 of developmental changes, coupled often with an enhanced degree 

 of mere growth. 1?he leaf is an outgrowth from the super- 

 ficial part of the axis, consisting in its fully developed state 

 of cellular tissue, encompassed by epidermis and traversed by 

 fibro -vascular tissue. The cellular and fibrous elements either 

 become detached from the axis at about the same level or at 

 considerably different levels. The term concrescence, as used 

 by Van Tieghem, is more in accordance with the actual facts of 

 the case. The < 



of Frenela and Callitris being especially remarkable for the 

 extreme degree to which the apparent union is carried *. 



Among the Lycopodiaceae, L. casuarinoides is noteworthy for 

 the resemblance in the arrangement of its leaves to that of 

 Callitris. In the "pulvinus" of Picea, the cellular portion, 

 though not fully separated, becomes prominent at some distance 

 beneath the point where the vascular cords leave the axial 

 cylinder ; hence a section of the pulvinus shows it to be cellular 

 for nearly all its length and to be rather a production from the 

 cortex than an essential part of the leaf f. The pulviui there- 

 fore require to be distinguished from ordinary " decurrent M 



* See Parlatore, Studi Organografice .... delle Conifere (1864), tab. 3. 

 f . 45. 









egree 













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t Masters in Journ. Linn. Soc., Botany, vol. xvii. p. 547 (1879). 





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