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DK. M. T. MASTEBS ON THE MORPHOLOGY, 

















spora tetragona aurea (a form of Thuya obtusa), the median and 

 the lateral leaves are equally conduplicate, so that the branch 

 system is four-cornered instead of flattened as it usually is in the 

 genus Thuya, and which finds a parallel in the case of Lycopodium 

 telragonum. In other forms of Thuya, such as T. plicata and 

 T. Wareana, hort., the lateral leaves (always flattened) are so in- 

 ordinately so that they become almost like the median ones in 

 appearance. In Sequoia gigantea, Taxodium distichum, and Fitz- 

 roya patagonica the leaves are all of one pattern throughout. On 

 the other hand, in the so-called genus Retinospora, comprising 

 species belonging to the genera Thuya, Charncecyparis, and Juni- 

 perus, the leaves may occur in three or more different forms. In- 

 dividual plants propagated by grafting or cuttings may present 

 one type of foliage only, and thus it is that different species and 

 even a separate genus have been created on what are only forms 

 peculiar to certain stadia or stages of growth. Two or more 

 forms have been observed on the same plant, or the plant has 

 been watched from the seedling state and the pleiomorphism thus 

 detected. 



Engelmann * mentions seven descriptions of leaves in Pinus : 

 1, cotyledons; 2, primary leaves; 3, bud-scales, which he calls 

 bracts ; 4, the true oe secondary leaves ; 5, the scales constituting 

 the sheath of the fascicles of leaves ; 6, the bracts of the male 

















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inflorescence ; and 7, the bracts outside the carpellary scales. 

 These seven may, however, all be reduced to tw r o categories, leaves 

 and leaf -scales. 



There is a frequent correlation between the form of the branch 

 and that of the leaves ; thus, in Libocedrus tetragona the 

 branches are subterete and the leaves uniform in shape, 

 spreading and regularly arranged in four rows. Similar regu- 

 larity of form and disposition occurs in Taxodium distichum var. 

 imbricaria, in Thuya jilif era, hort., Abies Pinsapo, &c. On the 

 other hand, where the branches are flattened, either from side to 

 ide or in the median plane, the leaves are generally appressed 

 and unequal in size, the median ones being smaller and flatter 

 than the lateral ones, which are often conduplicate. In Libocedrus 

 Doniana the sterile branches are flattened and bear appressed 

 dimorphic leaves ; the fertile branches bear spreading leaves only, 

 and these pass by imperceptible gradations into the scales of the 



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* Engeliuann, Kevision of the Genus Pinus. p. 163. 



















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