Altitudinal variation of resin ducts in Pinus taiwanensis Hayata (Pinaceae) needles
The variation of resin ducts in needles of Pinus taiwanensis along an altitude gradient (700 m- 3,100 m) in central Taiwan is revealed for the first time in this study, including position type, number, size, arrangement pattern and anatomical structural variation. Three types of resin ducts-medial, external and septal-were found according to their relative positions in the mesophyll. All needles sampled showed combinations of these three resin duct types. Mostly, 3-7 resin ducts were found in the mesophyll per needle, and the number of resin ducts was significantly greater at mid altitudes than at high and low altitudes. Septal ducts decreased in number with an increase in altitude; however, needles from mid altitudes had more external ducts. Eight patterns (basic and patterns I-VII) of resin ducts in the mesophyll of needles were delineated to present the arrangement variations. In addition to the primary ducts found in the mesophyll, we found the rare bundle sheath ducts in some needles, and their frequencies decreased obviously with an increase in altitude. The consistent combination feature of medial, external, and septal ducts in needles of P. taiwanensis from Taiwan could be easily distinguished from those with medial ducts from mainland China. However, this difference has unrecognized before, and it should be considered in future taxonomic work.
Anatomical Studies of the Leaf Structure of Chinese Pines
The comparative anatomy of the leaves of 23 species, 4 varieties and 4 forms of the genus Pinus has been investigated with special reference to their transverse sections and epidermal structures. Following a brief description of each species, a key to such is proposed. The stomata of these species can be classified into two types, each represented by P. koraiensis (Haploxylon) and P. tabulaeformis (Diploxylon) respectively. Based on the fact that the epidermal character is intimately correlated with the arrangement of the "connecting cells" in the stomata, it is reasonable to subdivide the genus Pinus into two subgenera. Likewise, the characteristics of the hypodermis, the position and number of the resin ducts, and the nature of endodermis are important criteria for the identification of these two subgenera. The systematic position of P. bungeana Zucc, P. yunnanensis Franch. var. tenuifolia Cheng et Y. W. Law, and P. kwangtungensis Chun has also been discussed.
Oviposition preferences in pine sawflies : a trade-off between larval growth and defence against natural enemies
The oviposition preferences and performance of a monophagous pine sawfly (Neodiprion sertifer) were studied in the field on 61 naturally regenerated Scots pine trees. The preference of sawfly females, measured as the proportion of available shoots on a tree with egg batches, was found to be positively correlated with tree height and needle length in a multiple regression analysis. Females also seemed to prefer trees with high resin acid (diterpenoid) concentrations. Low variation among trees with respect to resin acid concentration, together with positive covariance between these concentrations and needle length, made it difficult to evaluate the role of resin acids. Even though pupae weighed less and larvae suffered higher mortality when protected from natural enemies on trees preferred by females, there were benefits associated with oviposition on such trees; i.e. uncaged larvae were less vulnerable to parasitoids on high resin acid trees. This indicates that females preferred trees on which their offspring gained enemy-free space over trees on which performance was high, which also was suggested by the weak interaction found between the effect of caging (enemy exposure) and oviposition preference on survival in early instars.