LEAF DIMORPHISM IN POPULUS TRICHOCARPA

Critchfield , William B. (Pacific SW Forest & Range Expt. Sta., Berkeley, Calif.) Leaf dimorphism in Populus trichocarpa. Amer. Jour. Bot. 47 (8) : 699–711. Illus. 1960.—In Populus trichocarpa and other species of Populus, each tree bears 2 kinds of leaves, referred to here as “early” and “late” leaves. Both leaf types are present on all long shoots. They differ in many features of external morphology, including petiole length, size and occurrence of marginal glands, venation, and stomatal distribution. This type of foliar dimorphism has its origins in a pronounced difference in leaf ontogeny. The early leaves originate in the developing bud and overwinter as embryonic leaves. The first late leaves are also present in the winter bud, but as arrested primordia, and succeeding late leaves are initiated at the tip of the growing shoot and develop uninterruptedly to maturity during the growing season. A similar correlation between leaf form and the circumstances of leaf ontogeny appears to be a common feature of many other instances of heterophylly. The expansion of the pre-formed early leaves is almost completed by late spring, when the first late leaves begin to grow rapidly. The formation of late leaves may then continue until late in the season. The rapid elongation of the stem does not begin until the first late leaves expand. Elongation is restricted to shoots producing late leaves. Consequently, the early leaves are confined to short shoots and the base of long shoots; adventitious shoots and the upper part of long shoots bear only late leaves. Certain other woody plants with long and short shoots also exhibit a restriction of elongation to those shoots on which a second set of leaves is produced.     

Testing a new hypothesis: plant vigor and phylloxera distribution on wild grape in Arizona

Summary Longer, meaning more vigorous, shoots of a wild grape clone (Vitis arizonica) were more susceptible to attack by second and third generations of leaf-galling grape phylloxera,Daktulopsphaira vitifoliae, as the growing season progressed. Although there was no significant difference in mean shoot length between attacked and unattacked shoots within a clone at the beginning of shoot elongation, attacked shoots were significantly longer than unattacked shoots when elongation had ceased (P<0.01). Also, long attacked shoots had a significantly greater population of phylloxera galls than short attacked shoots (P<0.01) as the season progressed. The phylloxera population on long shoots increased rapidly while the population on short shoots remained the same. Longer shoots also produced significantly more axillary shoots than shorter shoots as the season progressed (P<0.001), and the number of axillary shoots accounted for 66 percent of the variance in number of attacked leaves on a shoot. Experimental evidence showed that there was a significantly greater percentage of available leaves attacked on long shoots than on short shoots (P<0.05) and the leaves on long shoots generally had a greater number of galls per leaf. The relationship between shoot length and probability of attack was also tested by comparing shoots lengths of 10 attacked clones and 10 unattacked clones at a second location. Mean shoot lengths of attacked clones were significantly longer than mean shoot lengths of unattacked clones (P<0.05), and mean shoot lengths of attacked shoots within a clone were significantly longer than unattacked shoots (P<0.001). Longer shoot length accounted for 81 percent of the variance in probability of attack. The reason for this pattern of attack was that long shoots produced newly expanding leaves over a longer time during the growing season and multivoltine phylloxera require undifferentiated tissue to initiate gall formation. Patterns of attack within a shoot were characterized by an uneven distribution of galls among leaves. This was due to development time between generations and the current availability of undifferentiated tissue at times of colonization. This study supports the hypothesis that some herbivore species are favored more by vigorous plants than by stressed plants.     

云南元江干热河谷木本植物的物候

在中国西南干热河谷的典型地段——元江干热河谷,连续3年观测了32种木本植物的枝条生长、叶片动态、花期、果期和果实类型。这些植物的枝条生长方式可以分为连续生长、枝条枯死、陡长和间歇生长4个类型。其中连续生长型占优势,包括13种植物,它们的枝条在雨季连续不断伸长。9种植物雨季的枝条伸长与连续生长型的相似,但它们顶部的枝条在旱季末期出现枯死现象。6种植物属于陡长型,在2周内完成抽枝,且一年只抽一次枝。4种植物属于间歇生长型,枝条在雨季来临后伸长一段时间,然后生长停滞,过一段时间后再接着伸长。从叶片物候类型看,元江干热河谷植被以落叶植物占优势。落叶植物中冷凉旱季（11月～2月）落叶植物占优势（19种）,而干热旱季（3—4月）落叶植物很少（4种）。除红花柴（Indigofera pulchella）和狭叶山黄麻（Trema angustifolia）从雨季中期开始脱落叶片外,其它30种植物从雨季末期开始脱落叶片,落叶期至少延续3个月以上。常绿植物脱落近1／3～1／2的当年生叶片。共有6种植物能在旱季末期长出新叶。常绿植物的叶面积、单个枝条上的总叶面积和枝条承载（总叶面积／枝条长度）比落叶植物小。虽然一年四季都有不同植物开花和结果,但多数植物（29种,占观测树种的91％）的花期集中在旱季和雨季初期,而果实（种子）成熟期从雨季末期延续到旱季末期和下个雨季初期。果实多为核果。     

花棒液流变化规律及其对环境因子的响应

在西北干旱沙区,采用茎流热平衡技术对花棒主茎、一级分枝和二级分枝液流进行研究.结果表明,在整个生长季内液流速率日变化曲线峰型表现各异,但在短时间段内其液流速率日变化有较强的规律性.主茎和一级分枝液流速率的曲线在生长季中期出现了剧烈动荡,在生长季末期到达最大值后同一数值维持较长时间;二级分枝的液流量在生长季初期出现了“昼低夜高”、生长季中期的液流量低于6、9月份液流量;主茎和一级分枝单日液流量的最大值出现在7月份,分别为5 781.6 g和3 180 g,二级分枝的最大值出现在9月份(480 g).日液流量大小依次为主茎>一级分枝>二级分枝,而液流通量在整个生长期内表现比较复杂.通过对同时观测的气象因子的分析,表明在整个生长季影响花棒液流速率的主导因子是土壤含水率,而在一个较短的时间段内,光照强度、气温和水汽压亏缺则是影响花棒液流速率的主导因子.     

Population dynamics,productivity and biomass allocation ofZizania latifolia in an aquatic-terrestrial ecotone

The population and production ecology of aZizania latifolia stand at a sheltered shore of the Hitachi-Tone River were investigated. Shoot emergence was observed twice a year; the fist was a synchronized shoot emergence in April and the second was from August to October. Aboveground biomass was mostly occupied by leaves and peaked at 1500 g dry weight m⁻² in August. The belowground biomass also reached its peak, 750 g dry weight m⁻², in August. The secondary shoots were small in spite of their high density. Leaves were produced continuously throughout the season. The leaf life span was as short as 55.6 days for cohorts that emerged from May through to September. Total annual net production ofZ. latifolia could be more than 3400 g dry weight m⁻². Shoot clusters of several centimeters were observed in April. The following self-thinning caused a regular distribution of the remaining shoots in August. Most shoots produced in August to October were found near a shoot persisting since April. They showed more concentrated distribution than shoots in April. A large biomass allocation to leaves and the ability to produce many clump shoots during the late growing period may facilitate dominance ofZ. latifolia in relatively sheltered sites.     

Ramet phenology and clonal architectures of the clonal sedge <Emphasis Type="Italic">Schoenoplectus americanus</Emphasis> (Pers.) Volk. ex Schinz &; R. Keller

The clonal plant Schoenoplectus americanus shows variable belowground clonal architecture as a result of producing two types of ramets: those with very long rhizomes (long rhizome ramet, LRR) and those with very short ones (short rhizome ramet, SRR). In a previous study we demonstrated that the two types of ramets are functionally specialised. The production of SRRs results in the formation of consolidated clonal patches with densely packed shoots, while the production of LRRs results in a more diffuse network of connected rhizomes with widely spaced shoots. We hypothesised that the two types of ramets would be produced at different times during the growing season because of their functional differences. The production of LRRs throughout the growing season would enable the species to continuously explore new habitats while the production of SRRs early in the growing season would enable the species to occupy and consolidate resources in available open patches. We evaluated this hypothesis through field observations in different communities with S. americanus and indeed found that SRRs were produced early in the growing season while LRRs tended to be produced over an extended period of time. Plants in high-quality environments (i.e. higher light conditions) produced more SRRs, and these were formed early in the growing season. In contrast, plants in low-quality environments produced more LRRs, and these were formed continuously over the growing season. We also observed that the shoot longevity was greater for SRR. In high-quality patches, the production of the lower cost SRRs results in a more rapid occupancy of open spaces; in lower quality patches, the production of LRRs throughout the growing season enables plants to explore the immediate environment for higher quality patches.     

Periods of organogenesis in mono- and bicyclic annual shoots of Juglans regia L. (Juglandaceae)

The organogenetic cycle of shoots on main branches of 4-year-old Juglans regia trees was studied. Mono- and bicyclic floriferous and vegetative annual shoots were analysed. Five parent annual shoot types were sampled between October 1992 and August 1993. Organogenesis of summer growth units was monitored between 16 Jun. and 3 Aug. 1993. Variations over time in the number of nodes, cataphylls and embryonic green leaves of terminal buds were studied. The number of nodes of parent shoot buds was compared with the number of nodes of shoots derived from parent shoot buds. The spring growth units of mono- and bicyclic shoots consist exclusively of preformed leaves which were differentiated, respectively, during the spring flush of growth (mid-April until mid-May) or the summer flush of growth (mid-June until early August) in the previous growing season. Thus, winter buds may consist of flower and leaf primordia differentiated in two different periods during annual shoot extension. The summer growth units of bicyclic shoots consist of preformed leaves that were differentiated in spring buds during the spring flush of growth in the current growing season. Bud morphology is compared between spring and summer shoots.     

SEEDLING MORPHOLOGY IN MARAH (CUCURBITACEAE) RELATED TO THE CALIFORNIAN MEDITERRANEAN CLIMATE

Studies in reproductive ecology were made in indigenous, western American plants in the genus Marah (Cucurbitaceae), with particular attention given plants of M. oreganus occurring in the Berkeley Hills near San Francisco Bay in California. These tuberous perennials produce capsular fruits on their annual aboveground shoots; the fruits dehisce in early summer, each one exposing about three large seeds with an average seed weight of 1.05 g. The embryo of a M. oreganus seed has two thick and fleshy cotyledons packed with protein granules. The embryonic axis, with shoot and root apices, is ca. 0.5-1.0 mm long, roughly ½0 or less the length of the seed. In the Berkeley Hills dispersal of the seeds is accomplished by nocturnal rodents, after which germination begins with the fall rains and cooler temperatures of November and December. Instead of a radicle emerging first from the seed at germination, the minute radicle and epicotyl are pushed or carried far out of the seed, down into the soil, by the elongating bases of the cotyledons. These cotyledon bases, or petioles, are fused, and as they elongate they form a hollow tube that bears the embryonic axis at its extreme tip. The cotyledonary petiole tube ceases elongation by January, when it may be 5-25 or more cm long in a seedling of M. oreganus. Then, from its tip, the radicle grows downward and the epicotyl upward—up the hollow petiole tube. The green shoot (epicotyl) reaches the soil surface by early March in this area, completes the first season's growth, and dries up by late May, when the arid summer season is beginning. But even before the epicotyl grows out of the petiole tube and above ground, the seedling's hypocotyl begins to enlarge, forming a tuber. The fleshy cotyledon blades remain in the seed coat below ground, and some food from the blades is transferred to the tuber that produces shoots in the following growing seasons. This pattern of germination and seedling establishment is now known for species of Marah and for a very few other dicotyledonous plants, all of them growing mainly in areas of hot and dry habitat that are generally referred to as having Mediterranean climate. This elongation of the fused hypogeal cotyledons is considered a complex adaptation in dicotyledons that helps ensure fast and successful seedling establishment in seasonally arid areas such as “Mediterranean” California.     

Osservazioni sul ciclo di sviluppo delle gemme di esemplari mascbili e femminili di Ginkyo biloba L.

Abstract

Observations on the development cycle of the buds of male and female specimens of Ginkyo biloba L. – A study of the buds of long shood and short shoot of male and female Ginkyo biloba L. individuals reveals the following: 1) All the buds of the male individuals are bigger and round in shape while those of the female individuals are smaller and conical. 2) Among individuals of the same sex there are no differences between the buds of long and short shoots except that the latter are always bigger. 3) All the buds, both male and female, show a constant number of buds scales (7–14), embryonic leaves (3–7) and leaf primordia (3–4). 4) The increase in diameters is greater in the male than in the female buds. 5) When opening, the buds of the male short shoots can get as big as 11,5 mm × 11,5 mm and those of the female short shoots 5 mmx4 mm. At this time, the long shoots of both sexes show a less marked differences in size (♂ 5 mm × 5 mm; 9 4 mm × 3,5 mm). 6) The male buds of both long and short shoots are always mixed, that is they are provided with a very small apex and pollen sacs. Only on exceptional cases has sterility been observed. On the other hand female buds are mixed, that is they are provided with a shoot apex and ovules, only in the long shoots of three or more years of age and not always; while the buds of the long shoots are always sterile. 7) Opening of the buds, which in both sexes occurs from the base upwards, takes place at the middle of March in the male and in the first decade of April in the female individuals. 8) The appearence of sex, starting from the base, takes place at an earlier time in male individuals. In fact in the buds of the male short shoots it appears as early as July. In the buds of the female short shoots it appears in October. 9) Pollen cones do not appear at the same time in all the buds of the two types of shoot. They are found in the buds of the short shoots in July, in October in the lateral buds of the long shoots and in November in the terminal buds of the same type of shoots. 10) Ovules appear only in some buds of short shoots three or more year old. They are never present in the long and short shoots one or two year old buds. 11) The dates of appearance of the pollen cones and ovules in our Florentine specimens are exactly the same as those reported by SPRECHER (1907) for the Ginkyo plants growing in Geneva.     

LEAF TURNOVER RATES OF ADENOSTOMA FASCICULATUM (ROSACEAE)

The age structure of the foliage of a 26-yr-old stand of Adenostoma fasciculatum H. & A. (chamise) was analyzed. The mean number of standing leaves and the yearly increase in leaf scars on the leaf-producing short shoots allowed an estimate of annual leaf production. The average chamise leaf persists for two seasons. Short shoots produce 4–6 leaves per yr; however after 4–5 yr their productivity declines. About 72% of the standing leaves were produced during the current and 28% during the foregoing season. Nearly one-half of all the leaves produced was found on current-year short shoots (i.e., on long shoots that had developed during the spring of the same year). Thus, earlier estimates of leaf production in chamise based only on current-year long shoot growth were too low.     

Shoot morphogenesis associated with flowering in Populus deltoides (Salicaceae)

Temporal and spatial formation and differentiation of axillary buds in developing shoots of mature eastern cottonwood (Populus deltoides) were investigated. Shoots sequentially initiate early vegetative, floral, and late vegetative buds. Associated with these buds is the formation of three distinct leaf types. In May of the first growing season, the first type begins forming in terminal buds and overwinters as relatively developed foliar structures. These leaves bear early vegetative buds in their axils. The second type forms late in the first growing season in terminal buds. These leaves form floral buds in their axils the second growing season. The floral bud meristems initiate scale leaves in April and begin forming floral meristems in the axils of the bracts in May. The floral meristems subsequently form floral organs by the end of the second growing season. The floral buds overwinter with floral organs, and anthesis occurs in the third growing season. The third type of leaf forms and develops entirely outside the terminal buds in the second growing season. These leaves bear the late vegetative buds in their axils. On the basis of these and other supporting data, we hypothesize a 3-yr flowering cycle as opposed to the traditional 2-yr cycle in eastern cottonwood.     

Shoot elongation,leaf demography and bud formation in relation to branch position on Larix laricina saplings

Summary Shoot development was investigated on branches of Larix laricina (Du Roi) K. Koch trees growing in their 8th year in two plantations and in a natural stand approximately 12 years old. Expansion of throughout-crown series of short and long shoots was measured weekly, and later colour change and natural fall of leaves were assessed. Similar shoots were collected at intervals and dissected, the long shoots by 25-leaf segments. Leaf area and weight, as well as time of bud formation, were determined. Increasing acropetal trends were evident in time to bud burst: duration of short-shoot leaf-cluster expansion; size of leaf clusters and number, area and weight of leaves per cluster; duration and rate of long-shoot elongation; number, area and weight of leaves on long shoots; time to terminal-bud formation on long shoots. Along each long shoot, stem and leaf elongation and lateral-axis formation progressed acropetally. Lateral axes were most numerous on second to fourth 25-leaf segments. On longer shoots, some axes in middle segments developed as sylleptic short shoots rather than as lateral buds. Leaves of short shoots and basal leaves on long shoots turned yellow and abscissed sooner than axial leaves on long shoots. Colour change and loss among axial leaves were acropetal along shoots and up the crown. Thus, last-formed leaves, in axils of some of which lastformed lateral buds occurred, were held longest.     

Dynamics of flower development and vegetative shoot growth in the high mountain plant Saxifraga bryoides L.

Saxifraga bryoides L. is an abundant species in the subnival and nival zone of the European mountains. First flowering occurs, at the earliest, 6 weeks after snowmelt. This is a remarkably long prefloration period in an environment with a short growing season. To gain more information about the developmental strategies of this species, the timing and the dynamics of flower bud formation and vegetative shoot growth were studied at sites with growing seasons of different lengths at two subnival locations (2650 and 2880 m a.s.l.) in the Tyrolean Alps. At an early, mid and late thawing site, individuals emerging from the winter snow were labelled. Reproductive and vegetative shoots were sampled at regular intervals throughout the growing season and analysed, using different microscopic techniques. Flower buds of S. bryoides develop in three cohorts. Provided the growing season is long enough, cohorts 1 and 2 come into flower, whereas cohort 3 buds remain primordial and continue to develop after winter. New flower primordia appear as day-length decreases from August on, which suggests a short-day requirement for floral initiation. At the end of the growing season, flower buds of different stages are present, but only primordial stages survive winter. Thus, flower buds of S. bryoides develop largely or even completely in the year of anthesis. Developmental dynamics were quite similar at the different sites. Time from flower initiation until anthesis took about 2 months, independently of whether flowers were formed within one or two seasons. All of the leaves on vegetative short-stem shoots turnover within a growing season. Leaves having passed winter continuously decline and are replaced by newly formed ones (21±3 at the mid-thawing site and 18±1 leaves at the short-season site). An individual leaf functions therefore, on average, about 12 months. In most years the seed crop of S. bryoides results mainly from the first cohort of flowers in an individual. In a changing climate with a prolonged growing season, the chance of two cohorts to develop mature seeds from flower cohorts 1 and 2 would increase.     

Crown hollowing as a consequence of early shedding of leaves and shoots

Leafing pattern has long been considered as an important element characterizing the growth strategy of tree species; however, the consequences of leafing pattern for tree-crown formation have not been fully understood. To address this issue, the dynamic events (growth, birth, and death) of current-year shoots and leaves were investigated together with their location in saplings of a pioneer tree, Alnus sieboldiana. The leafing pattern was characterized by successive emergence and shedding of short-lived leaves. The combination of successive leafing and within-crown variation in leaf production brought about characteristic outcomes in crown morphology. In the outer crown, because of continuous leaf production, the shoots achieved great extension and enormous daughter shoot production, resulting in rapid expansion of the crown. In contrast, in the inner crown, due to early termination of leaf production, the shoots completely lost their leaves early in the growing season and consequently themselves died and were shed within the season. Such quick shedding of shoots caused “crown hollowing”, i.e., the interior crown consisted of primary branches with little secondary development or foliage. These dynamic features are an effective adaptive strategy in early succession but also may be a disadvantage to maintaining foliage for longer period. Crown maintenance associated with the longevity of structural components is thought to play an important role in survival strategy of tree species.     

Variation in shoot mortality within crowns of severely defoliated <Emphasis Type="Italic">Betula maximowicziana</Emphasis> trees in Hokkaido,northern Japan

To clarify mortality patterns of current-year shoots within the crown of Betula maximowicziana Regel after severe insect herbivory in central Hokkaido, northern Japan, we investigated the degree of defoliation, pattern of shoot development, shoot mortality, and leaf tissue-water relations. One hundred current-year long shoots growing in a B. maximowicziana plantation were observed for defoliation and mortality in June 2002. An outbreak of herbivorous insects (Caligula japonica and Lymantria dispar praeterea) occurred in the stand in mid-to-late June, and the monitored shoots were defoliated to various degrees. Within 1 month of defoliation, some of the severely defoliated shoots had produced new leaves on short shoots that had emerged from axillary buds. Stepwise logistic regression revealed that the probability that current-year long shoots would put out axillary short shoots with leaves is closely related to the degree of defoliation. To evaluate the water relations of the leaves, we determined pressure–volume curves for the leaves that survived the herbivorous insect outbreak and the new leaves that emerged after defoliation. The water potential at turgor loss (Ψ_l,tlp) and the osmotic potential at full turgidity (Ψ_π,sat) were higher for the new leaves than for the surviving leaves, indicating a lower ability to maintain leaf cell turgor against leaf dehydration in the new leaves. Of the 100 shoots, 13 died after the emergence of new leaves. Stepwise logistic regression revealed that the probability that the long shoots would die generally increased with the emergence of new leaves, with increasing shoot height. This result suggests that the combined effect of the vulnerability of newly emerged leaves and low water availability, associated with higher shoot positions within the crown, caused shoot mortality. Based on our results, some possible mechanisms for mortality in severely defoliated B. maximowicziana are discussed.     

Growth responses of a woody species to clipping and goat saliva

Studies on the role of mammalian herbivore saliva in plant–animal interactions have mostly focused on graminoid species and bovine saliva. A trial was performed in Botswana with clipping treatments to simulate browsing of shoots and the application of goat saliva on the woody species Combretum apiculatum Sonder (Combretaceae). Treatments were performed during early growing season while shoot growth was rapid, and responses of trees were recorded later in the same season. Clipped shoots with saliva had significantly enhanced shoot growth (tripled in length) and leaf production (2.7 times more leaves) compared to clipped shoots without saliva. However, unclipped shoots still grew more than clipped shoots, with or without saliva treatment.     

Differences in Architecture and Shoot Growth during Stagnant and Extension Growth Phases of Acanthopanax sciadophylloides(Araliaceae)

The shoot growth of a deciduous tree, Acanthopanax sciadophylloidesFranch. et Savat. shows inter-annual intermittent repetitionof two distinctive phases, a stagnant growth phase (S-phase)and vigorous extension-growth (E-phase). To help understandthe differentiation mechanism, shoot development was studiedover time in both shoot phases. S-phase and E-phase shoots weredistinguished from each other by morphological traits: S-phaseshoots are characterized by higher allocation to leaves anda shorter period of stem growth, while E-phase shoots show continuousstem extension over the growing season. Specific leaf area didnot differ between the two phases. This shoot differentiationwas similar to the morphological differentiation of shoots betweenlong vs. short shoots found in some temperate trees. Leavesof both phases were well-dispersed through adjustment of petiolelength and leaf-blade size to reduce mutual shading within ashoot. Stem-wood density of current-year shoots was lower inE-phase compared with S-phase shoots. Leaves produced earlyin the season affected the growth phase of the following year.These results suggest that annual shoot differentiation of A.sciadophylloides was determined during the previous season andreflects leaf productivity in a given habitat during that growingseason. Copyright 2001 Annals of Botany Company Acanthopanax sciadophylloides, Araliaceae, biomass allocation, intermittent shoot growth, leaf display, shoot architecture, shoot differentiation     

Structural and hydraulic correlates of heterophylly in Ginkgo biloba

This study investigates the functional significance of heterophylly in Ginkgo biloba, where leaves borne on short shoots are ontogenetically distinct from those on long shoots. Short shoots are compact, with minimal internodal elongation; their leaves are supplied with water through mature branches. Long shoots extend the canopy and have significant internodal elongation; their expanding leaves receive water from a shoot that is itself maturing. Morphology, stomatal traits, hydraulic architecture, Huber values, water transport efficiency, in situ gas exchange and laboratory-based steady-state hydraulic conductance were examined for each leaf type. Both structure and physiology differed markedly between the two leaf types. Short-shoot leaves were thinner and had higher vein density, lower stomatal pore index, smaller bundle sheath extensions and lower hydraulic conductance than long-shoot leaves. Long shoots had lower xylem area:leaf area ratios than short shoots during leaf expansion, but this ratio was reversed at shoot maturity. Long-shoot leaves had higher rates of photosynthesis, stomatal conductance and transpiration than short-shoot leaves. We propose that structural differences between the two G. biloba leaf types reflect greater hydraulic limitation of long-shoot leaves during expansion. In turn, differences in physiological performance of short- and long-shoot leaves correspond to their distinct ontogeny and architecture.     

Development of shoot inHydrangea macrophylla II. sequence and timing

The development of axillary buds, terminal buds, and the shoots extended from them was studied inHydrangea macrophylla. The upper and lower parts in a nonflower-bearing shoot are discernible; the preformed part of a shoot develops into the lower part and the neoformed part into the upper part (Zhou and Hare, 1988). These two part are formed by the different degrees of internode elongation at early and late phases during a growth season, respectively. Leaf pairs in the neoformed part of the shoot are initiated successively with a plastochron of 5–20 days after the bud burst in spring. The upper axillary buds are initiated at approximately the same intervals as those of leaf pairs, but 10–30 days later than their subtending leaves. Changes in numbers of leaf pairs and in lengths of successive axillary buds show a pattern similar to the changes in internode lengths of the shoot at the mature stage. The uppermost axillary buds of the flower-bearing shoot often begin extending into new lateral shoots when the flowering phase has ended. The secondary buds in terminal and lower axillary buds are initiated and developed in succession during the late phase of the growth season. Internode elongation seems to be important in determining the degrees of development of the axillary buds. Pattern of shoot elongation is suggested to be relatively primitive. Significances of apical dominance and environmental conditions to shoot development are discussed.