Author: T. H. Ho
J Integr Plant Biol 1959, 8 (4): -.
In a preliminary note, the writer reported a fact that an unusual seasonal growth layer (sensu stricto, ex Ho) is present in the growth ring of Eucalyptus robusta Sm. which had been introduced in to Canton about the year 1920. The purpose of the present paper is to discuss further how the arrangement and occurrence and how the size and abundance of various woody cells of the given species are subject to the temperature and rainfall in the region of Canton. All the samples distributed into three growth ring groups were taken at 1.3 m above the ground and sectioned. Tangential sections were cut respectively from different portions, i.e., the inner part, the outer part (ibid.) and the unusual growth layer of a ring of the same sample which had been firstly used for preparing transverse section. The macerated material was similarly treated, but supplied with the supplementary sample. Microscopic projections were used for the most of the measurements made. The wood structure of the species cultivated was described in detail. Size and proportion of various woody cells between different portions of the same growth ring have been compared. In the cultivated area, Canton, the ascent and descent of temperature correspond to the increase and decrease of the rainfall. However, in the native place, the coast of New South Wales, when rainfall begins to decrease in August, the temperature is relatively high (but in December, rainfall increases again), and when the rainfall increases to 100 mm in February, then the temperature is relatively low. In Canton, the range between the extreme values of extreme highest and lowest temperature is 38℃, the extremum reaches –0.3℃, the continentality is 46.7, and a striking contrast between rainy season and dry season exists. From July to August typhoon sweeps here. All the factors listed are not those of the native place of E. robusta in Australia.
At present, distinct growth rings have not been formed in E. robusta here, but it has a layer of unusual growth at the rear of a ring or at the ring boundary. (For the presence and the width of this layer please refer to the previous paper). The difference between both the inner and outer parts and the unusual layer occur in the 15th ring group. The presence of “vesselless zone” between this group and the neighbouring one is only 19.2% .
For tangential diameter of solitary pores, number of pores and pore groups, the pore area and vessel member length, vessels of the unusual growth layer are more developed than those of both inner and outer parts; in turn, the inner more than the outer. Generally .speaking, on the ray width and ray height, rays of the unusual layer are more developed than those of the outer or the inner part, and the outer more than the inner; the number of rays in the inner part is less than or equal to the outer, but both the parts are more than that in the unusual layer; the percentage of uniseriate rays in the outer part or the unusual layer is more than that in the inner. In regard to the fibre length, fibres of the outer part are longer than those of the inner; in turn, fibres of the inner longer than those of the unusual layer. These mentioned quantitative features especially in regard to the vessel and fibre may be explained that the unusual growth layer of E. robusta here corresponds to its inner part, i.e., the early wood formed in the Australian native place.
According to the growth ring and woody elements of this introduced Eucalypt and from references, the present writer is still to think that both inner and outer parts of the Eucalypt are subject to the influence of the environment, however, the unusual seasonal growth layer represents its nature which has not yet changed wholly.