Illustrations of Conifers. 71 



THUYA. 



EVERGREEN trees of pyramidal habit belonging to the tribe Cupres- 

 sineae of the order Coniferae. Branches spreading, terminating in 

 flattened pinnately divided " branch systems " which are densely 

 clothed with scale-like leaves. The leaves are arranged in four 

 ranks, in two decussate pairs, those of the lateral ranks being boat- 

 shaped, the dorsal and ventral ones flattened. In the seedling state 

 the foliage is acicular and spreading. 



Flowers monoecious, all solitary and terminal on the ultimate 

 short branchlets of the previous year, the males consisting of three 

 to six pairs of decussately arranged stamens. Cones solitary, composed 

 of six to twelve imbricated scales in decussate pairs, the larger pairs 

 only fertile and bearing two to five seeds at the base. 



The Thuyas resemble the flat-leaved cypresses in habit and 

 foliage. The latter are best distinguished by their fruit which 

 consists of peltate and not imbricated scales. In the determination 

 of the species the arrangements of the branch systems give good 

 marks of distinction. In Thuya orientalis the branchlets stand in 

 vertical planes ; in the three other species they are arranged in hori- 

 zontal planes. The leaves on the main axes also afford useful dis- 

 tinguishing characters. They differ as follows : 



1. Thuya plicata, D. Don, North America. Leaves widely spaced, long, ending in long, 

 fine, free points which are parallel to the axis ; glands inconspicuous or absent. Under 

 surface of the foliage usually marked with white streaks. 



2. Thuya japoni-ca, Maximowicz, Japan. Leaves closely arranged. Shoots ending in 

 short, rigid, thick, triangular points, directed outwards at an acute angle ; glands absent. 

 Uuder surface of the foliage conspicuously marked with broad white streaks. 



8. Thuya occidental, Linnaeus, North America. Leaves widely spaced ; ending in long, 

 fine points which are parallel to the axis ; glands raised, large and conspicuous on the flat 

 leaves. Under surface of the foliage pale green ; white streaks inconspicuous or absent. 



4. Thuya onentalis, Linnaeus, China. Leaves widely spaced, ending in short, triangular, 

 free points which are not rigid and are directed slightly outwards at an acute angle; flat 

 leaves marked by longitudinal glandular depressions. Under surface of the foliage pale 

 green without white streaks. 



