Compensation of seed production after severe injury in the short-lived herb Barbarea vulgaris

A pot experiment with the common ruderal herb Barbarea vulgaris (Brassicaceae) was set up to elucidate to what extent short-lived species sprouting from roots regenerate and compensate for seed production after damage. We tested if sprouting from roots ensures survival after severe aboveground biomass damage, but the number of seeds produced declines with increasing severity of injury, decreasing nutrient availability and progress in the life cycle at the time of injury.Plants of B. vulgaris were cultivated in a 3-year garden experiment at two nutrient levels (high vs. low). During the experiment, two levels of injury severity were applied: high (removal of all aboveground biomass) and low (removal of aboveground biomass leaving basal axillary buds intact). Damage was applied at four life-cycle phases: young rosette, overwintered rosette, flowering plant and fruiting plant. All injured plants survived and resprouted irrespective of life-cycle phase, severity of injury and nutrient availability. Injury significantly affected seed production and also the plants’ life cycle. Plants injured in the second year of their life (overwintered rosette, flowering plant and fruiting plant) postponed reproduction to the third season (in the case of high injury severity) or their seed production was lower than in intact plants (in the case of low injury severity). In plants injured in the first life year, seed production and life cycle were not influenced. Nutrient level only marginally affected resprouting after injury and seed production.The experiment showed that the ability to sprout from roots enables plants to survive a 100% loss of aboveground biomass, and to keep some seed production or even compensate it. The short-lived ruderal species B. vulgaris successfully copes with severe disturbance by resprouting and does not rely only on its seed bank.     

Occurrence of adventitious sprouting in short-lived monocarpic herbs: a field study of 22 weedy species

Background and Aims

Adventitious sprouting from the hypocotyle and roots in monocarpic herbs has been confirmed in previous experimental studies as a means to avoid bud limitation after severe injury in annual and biennial plants. Data regarding the role of adventitious sprouting in natural populations, however, were lacking. The aim of the present study was to assess whether adventitious sprouting occurs in natural populations and how it is affected by plant size, plant injury, plant cover and environmental characteristics.

Methods

Data were sampled from 14 037 individual plants from 389 populations belonging to 22 annual and biennial species. Growth parameters were measured in individual plants, species composition and plant cover in communities were evaluated, and environmental characteristics were estimated using Ellenberg indicator values.

Key Results

It was confirmed that adventitious sprouting occurs in natural populations of all but five species examined. Adventitious sprouting was positively affected by plant size and plant injury. Environmental factors including availability of soil nitrogen were not shown to affect adventitious sprouting. Annual and biennial plants did not differ in sprouting, but upright annuals had a lower number of and longer adventitious shoots than prostrate annuals.

Conclusions

Adventitious bud formation is used to overcome meristem limitation when stem parts are lost due to injury, and thus resprouting in short-lived monocarps should not be overlooked.     

High Frequency Plant Regeneration from Astragalus melilotoides hypocotyl and stem explants via somatic embryogenesis and organogenesis

An efficient and reproducible procedure is established for the plant regeneration from hypocotyl explants and hypocotyl-or stem-derived calli in Astragalus melilotoides. High frequency somatic embryo formation (98.3%) occurred direct on hypocotyls on Murashige and Skoog (MS) medium supplemented with 2.69 µM NAA and 4.44 µM BA within 5 weeks. Three types of calli were induced from the hypocotyl and stem segments on MS medium containing 9.05 µM 2,4-D and 2.22–4.44 µM BA. Both somatic embryos and adventitious buds were initiated from hypocotyl-derived calli while only adventitious buds were formed from stem-derived calli in MS medium supplemented with 2.69 µM NAA and 4.44–8.89 µM BA. Somatic embryos or adventitious buds developed into plantlets following being cultured for 3 weeks on MS medium without any growth regulators or with 14.78 µM IBA, respectively. All the regenerated plants were normal with respect to morphology and growth characters, and produced fertile seeds after planting in soil.     

Vegetative regeneration of biennial Oenothera species after disturbance: Field observations and experiment

It has been recently shown that some annual and biennial species of man-made habitats cope with severe disturbance by resprouting (vegetative regeneration) from their bud bank and do not only rely on regeneration from seeds. Nevertheless, information on the ecology of this phenomenon is rare. In a field study, we answered the question how frequent is resprouting from root buds in populations of the ruderal biennial herb Oenothera biennis, and how it is affected by habitat conditions. In an experiment, we tested the hypothesis that higher severity of injury and later life-cycle phase of the injured plants suppress resprouting from both axillary and root buds in O. biennis and also in its closely related congeners O. fallax and O. glazioviana.In 25 out of 29 studied ruderal populations of O. biennis severely injured individuals were found; however, only half of these populations included injured individuals that resprouted from roots. Among these populations, the number of root-sprouting individuals varied highly (from 3% to 67% of injured individuals). The largest populations and the highest percentage of root-resprouting individuals were found in urban habitats with sandy/gravelly substrate, a low vegetation cover, and a high frequency of disturbance.In the experiment with three Oenothera congeners, removal of aboveground biomass with all axillary buds largely led to the death of plants of all three species. When a portion of the basal axillary buds remained intact, individuals of O. biennis mostly failed to regenerate, whereas individuals of O. fallax and O. glazioviana survived and formed seeds. A higher severity of injury suppressed resprouting in Oenothera congeners in this experiment. However, the relationship between life-cycle phase and the ability to resprout remains unclear in Oenothera species.This study showed that resprouting after severe injury is an important feature of Oenothera individuals occurring in man-made habitats and may represent an alternative strategy to regeneration from the seed bank under disturbance conditions.     

Resprouting after disturbance in the short-lived herb Rorippa palustris (Brassicaceae): an experiment with juveniles

The impact of plant age, severity of injury and nutrient levels on the ability to resprout from roots was experimentally assessed in juveniles of the short-lived herb Rorippa palustris (L.) Besser. In a chamber experiment, six cohorts of young plants (1–6 week old) were injured to obtain data on the threshold age for the ability to resprout from roots. We found that plant age was an important factor influencing resprouting ability: injured individuals older than 5 weeks were able to resprout, but not plants younger than 3 weeks. The impact of injury severity (defoliation and removal of axillary buds) and nutrient levels on resprouting ability was assessed on juveniles in a greenhouse experiment. Injury induced growth of new shoots from root buds, while the number of adventitious buds on roots was not influenced by injury. Both injury treatments had a similar effect in this respect, and the amount of regenerated biomass and the extent of regeneration were not different among injury treatments. The number of new shoots produced after injury was higher at the high nutrient level, but the number of formed adventitious buds on roots was not influenced by nutrient level. Nutrient level also influenced the amount of regenerated biomass, but the extent of regeneration (regenerated/removed biomass) was not influenced. The short-lived monocarpic species R. palustris is able to resprout from roots relatively easily. This ability seems to be advantageous in disturbed habitats and this idea is discussed throughout the paper.     

Efficient regeneration of plants independent of exogeneous growth regulators in bell pepper (Capsicum annumm L.)

Summary Organogenesis of shoots of bell pepper (Capsicum annuum L.) was achieved in fourteen cultivars on Murashige and Skoog's medium (MS medium) supplemented only with 0.4% (w/v) Gellan gum (pH 5.8). Mature seeds of cv. Shinsakigake-2 were sown on filter paper that had been wetted with sterilized water and precultured for zero to five days in under 16 hr of light per day at 25 °C. Explants, consisting of the proximal part of the hypocotyl and the radicle, were excised from the seeds and formed adventitious buds around the cut surfaces of elongated hypocotyls after four weeks of culture. When explants were subcultured on MS medium, 57% of the explants that had produced adventitious buds extended shoots after an additional three weeks of culture. Shoots were rooted on MS medium after two further weeks of culture. Chromosome numbers of all 30 regenerated plants that weexamined were normal (2n=24). The morphology of the mature plants was also normal and they set normally shaped fruits with mature seeds. Regenerated whole plants were also obtained in the case of 13 other cultivars by applying this simple procedure.Abbreviations MS Murashige and Skoog     

Regeneration capacity from buds on roots and rhizomes in five herbaceous perennials as affected by time of fragmentation

Variation in seasonal sprouting pattern from roots and rhizomes of perennial herbaceous plants influence the success of plant proliferation ability, invasiveness and escape from weed control measures. The latter often rely on methods, which repeatedly fragment the underground system, thereby trigger adventitious and axillary buds to sprout, and consequently reduce the amount of stored energy. If carried out at times when no re-growth occurs, treatments will have little effect on weed populations, but cost much in terms of labour and energy. The purpose of this experiment was to determine the seasonal variation in bud sprouting capacity after fragmentation. Five troublesome perennial weed species, collected in northern and southern Sweden, were grown outdoors in Uppsala, Sweden (N 59°49′, E 17°39′), from May 2009 to January 2010. Cut root and rhizome fragments, taken at two weeks intervals from July to January, were used to evaluate bud sprouting capacity, which was statistically analyzed using generalized additive models. In Elytrigia repens from southern Sweden and Sonchus arvensis sprouting capacity was significantly impaired during a period from September to November. In Equisetum arvense and Tussilago farfara sprouting was low between July and November where after it increased. In contrast, Cirsium arvense and E. repens from northern Sweden sprouted readily throughout the period. Except for E. repens, a model by populations was significantly better than one based on latitudinal origin. The result suggests a species-specific timing of treatments in weed management, avoiding the non-effective autumn period for E. arvense, S. arvensis and T. farfara, and in some cases in E. repens.     

柑桔实生苗大量增殖研究

将枳和酸橙的实生试管苗上、下胚轴和子叶切割成若干段分别进行离体培养,结果表明,枳的各个切段在添加10^-4或5×10^-5摩尔BA的MS培养基中,不定芽形成率最高,平均每个外植体不定芽发生总量分别达41个和33.5个,其中以上胚轴发生的不定芽最多,占全部不定芽总量的66.6%。在上、下胚轴中,则以第一切段发生的不定芽最多。添加KT的所有处理,不定芽均较少,形成不定芽最多的处理也仅及N₀B₁处理的四分之一。发根量则以添加10^-5摩尔NAA的培养基最多。将枳的不定芽扦插于添加5×10^-6或10^-6摩尔NAA的MS培养基中,15-20天即可发根成苗。在完全相同的各个处理中,酸橙的不芽定形成量明显少于枳。     

Assessment of Regeneration Potential in the Clonal Macrophyte Miscanthus sacchariflorus (Poaceae) after Burial Disturbance Based on Bud Bank Size and Sprouting Capacity

The demography of the bud bank and its sprouting capacity are important for understanding the population dynamics of clonal plants and their potential responses to disturbances. To this end, we investigated the size and composition of the bud bank of Miscanthus sacchariflorus (Maxim.) Hack. immediately after flooding (November), in winter (January), in spring (March), and before flooding (May) in the wetlands of Dongting Lake. We then examined the sprouting capacity of axillary buds after sediment burial at 0, 5, 10, 15, and 20 cm. Total bud density of M. sacchariflorus ranged from 2524 buds m^-2 in November to 4293 buds m^-2 in March. Rhizome segments with inactive axillary buds, which represented the majority of the bud population (88.7% in November, 93.3% in May), did not sprout during the 140 days of the experiment (n = 250). The sprouting ratio was the highest for active axillary buds buried at 0 cm (64%) and decreased when buried at 10–20 cm (34%–40%). Due to the large number of active axillary buds in the bud bank (211–277 buds m^-2 from November to the following March), M. sacchariflorus could completely replace its aboveground shoot population, except in May (142 buds m^-2). Increasing burial depth delayed bud emergence and reduced the growth period of shoots; however, burial depth did not affect the resulting plant height and only reduced the accumulated biomass at 20 cm. Therefore, the belowground bud bank and its strong sprouting capacity are important factors in the maintenance of local populations and colonization of new habitats for M. sacchariflorus after burial disturbances. The present methodology, which combined measurements of bud bank demography and sprouting capacity, may reflect the regeneration potential of clonal plants after burial disturbances.     

Checklist of root-sprouters in the Czech flora: mapping the gaps in our knowledge

The production of shoots from roots (adventitious bud and shoot formation, root sprouting) first attracted attention in the 19th century as a morphological rarity. At that time, the first checklists of plants capable of root sprouting were compiled. Since then, experiments have proven that the ability to produce buds on roots serves the purpose of bud bank formation or represents a mode of clonal growth. The former enables resprouting after injury whereas the latter facilitates foraging for nutrients and vegetative multiplication. However, only a small proportion of root-sprouters have been studied so far, and for most of them we lack detailed data on the anatomy, morphology, ecology and physiology of adventitious shoot formation. These knowledge gaps hinder further understanding of their ecology and evolution. To support researchers interested in adventitious bud and shoot formation in any field of plant science, we compiled a list of plants considered capable of root sprouting based on the literature and the CLO-PLA database for the flora of the Czech Republic. Here we provide basic comparisons concerning the distribution of root sprouting ability among life history types, plants differing in rarity and invasive status, and taxonomic groups. Altogether 342 plant species are reported to be root-sprouters, i.e. 10% of the Czech flora. Root-sprouters are most commonly found among woody plants, less so among non-clonal perennial herbs, biennials and clonal herbs, and least commonly among annuals. Root-sprouters are more common among alien plants (especially woody ones) than among red-listed plants. Root sprouting usually plays a supplementary (facultative) or regenerative role in the plant life cycle. Root-sprouters occur in 64 families, mostly of dicots. The greatest number of root-sprouters belong to the Asteraceae and Rosaceae families (41). We have only rudimentary information on 145 species out of the 342 (42%) species that are regarded as root-sprouters.     

In vitro organogenesis from root culture segments of Bixa orellana L. (Bixaceae)

The organogenic potential of root explants derived from cultured seedlings of Bixa orellana L. (annatto) was investigated in response to different incubation conditions and either 4.44 μM 6-benzyladenine, 4.54 μM Thidiazuron, or 4.56 μM Zeatin. Explants cultured in liquid media with agitation generally showed better development of adventitious buds versus explants cultured on semi-solid media. The most adventitious buds developed from explants cultured in liquid media under a 16-h photoperiod. Use of Zeatin and Thidiazuron promoted the development of more adventitious buds than 6-benzyladenine but morphological abnormalities among regenerating shoots and plants were observed. Fewer adventitious buds developed from explants cultured in liquid media supplemented with 6-benzyladenine, but the buds gave rise to the highest percentage of morphologically normal regenerated plants. Histological analyses showed that adventitious buds originated from cell proliferation within the pericycle, opposite the protoxylem poles of the explant. Seedling root tissue is useful for in vitro propagation of B. orellana.     

Growth and Dormancy Cycles in Citrus Bud Cultures and Their Hormonal Control

An in vitro bud culture method was devised in order to better understand the control mechanism of Citrus bud development. This technique offers a new approach to the study of hormonal control of growth, dormancy and flowering cycles in perennial plants. Buds were excised from orchard trees throughout the year, cultured on defined media for prolonged periods, and their vegetative growth responses to various growth hormones were determined. The buds proceeded with their vegetative development in vitro and achieved sprouting on a basal medium. The various growth regulators affected both the time required for sprouting (TRS) and the type of growth. In summer buds, IAA delayed sprouting, while GA enhanced it and caused shoot elongation. Cytokinins specifically induced the formation of numerous adventitious buds, whereas ABA completely inhibited sprouting; this inhibition, however, was reversible. A marked decrease in total protein and in the rate of its synthesis was evident during the first 20 days of sprouting induction and early bud growth. The annual growth rhythm was determined in spring buds sampled and cultured throughout the year, and an innate dormancy of citrus buds was revealed. Both the dormancy and the sprouting periods of buds in vitro corresponded to the natural periods occurring under field conditions. The effect of exogenous IAA, GA and cytokinins on the TRS varied at different periods along the season, suggesting the concept of “critical levels” in the endogenous balance of hormones.     

Effects of Aspect on Clonal Reproduction and Biomass Allocation of Layering Modules of Nitraria tangutorum in Nebkha Dunes

The formation of many nebkha dunes relies on the layering of clonal plants. The microenvironmental conditions of such phytogenic nebkha are heterogeneous depending on the aspect and slope. Exploring the effects of aspect on clonal reproduction and biomass allocation can be useful in understanding the ecological adaptation of species. We hypothesized that on the windward side layering propagation would be promoted, that biomass allocation to leaves and stems of ramets would increase, and that the effects of aspect would be greater in the layering with larger biomass. To test these hypotheses, we surveyed the depth of germination points of axillary buds, the rate of ramet sprouting, the density of adventitious root formation points, and the biomass of modules sprouting from layering located on the NE, SE, SW and NW, aspects of Nitraria tangutorum nebkhas. The windward side was located on the NW and SW aspects. The results indicated that conditions of the NW aspect were more conducive to clonal reproduction and had the highest rate of ramet sprouting and the highest density of adventitious formation points. For the modules sprouting from layering on the SW aspect, biomass allocation to leaves and stems was greatest with biomass allocation to adventitious roots being lowest. This result supported our hypothesis. Contrary to our hypothesis, the effects of aspect were greater in layering of smaller biomass. These results support the hypothesis that aspect does affect layering propagation capacity and biomass allocation in this species. Additionally, clonal reproduction and biomass allocation of modules sprouting from layering with smaller biomass was more affected by aspect. These results suggest that the clonal growth of N. tangutorum responses to the microenvironmental heterogeneity that results from aspect of the nebkha.     

Another evidence for inhibitory effect of auxin in adventitious bud formation of decapitated flax (Linum usitatissimum L.) seedlings

Adventitious buds were formed on the hypocotyls of decapitated flax seedlings. Scanning electron and light microscopic examinations of hypocotyls showed that epidermal cells divided to produce meristematic spots from which several leaf primordia were formed. Between leaf primordia and the original vascular tissues of hypocotyls, new xylem cells were formed which connected them. About 10, 30 and 60% of adventitious buds were formed on upper, middle and basal parts of hypocotyls of decapitated seedlings, respectively. Removal of apical meristem together with longer hypocotyl zero to four cm long below the apical meristem) induced higher percentage of adventitious bud formation in the remaining hypocotyl. When the entire hypocotyl was cut into 16 segments (0.25 cm each) and these segments were cultured on MS medium containing 3% sucrose and 0.8% agar, adventitious buds were mainly formed in the lowest five segments. These results suggested that there was a gradient of inhibitory factor(s) from apical to basal part of hypocotyl with respect to adventitious bud formation. Auxin transport inhibitors, morphactin and TIBA induced adventitious bud formation on intact seedlings by suppressing the basipetal movement of auxin.     

Comparative analysis of root sprouting and its vigour in temperate herbs: anatomical correlates and environmental predictors

Background and AimsRoot sprouting (RS), i.e. the ability to form adventitious buds on roots, is an important form of clonal growth in a number of species, and serves as both a survival strategy and a means of spatial expansion, particularly in plants growing in severely and recurrently disturbed habitats. Occurrence and/or success of plants in severely and recurrently disturbed habitats are determined by two components, namely the ability to produce adventitious buds on roots and the vigour of their production. As mechanisms behind different magnitudes of RS remain unclear, our study investigates: (1) whether the presence or absence of specific tissues in roots can promote or limit RS; and (2) whether there is some relationship between RS ability, RS vigour and species niche.MethodsWe studied RS ability together with RS vigour in 182 Central European herbaceous species under controlled experimental conditions. We used phylogenetic logistic regressions to model the presence of RS, RS vigour, the relationship between RS and anatomical traits and the relationship between RS and parameters of species niches.Key ResultsA quarter of herbs examined were able to produce adventitious buds on roots. They were characterized by their preference for open dry habitats, the presence of secondary root thickening and the occurrence of sclerified cortical cells in roots. Root sprouting vigour was not associated with any specific anatomical pattern, but was correlated with the environmental niches of different species, indicating that preferred disturbed and dry habitats might represent a selection pressure for more vigorous root sprouters than undisturbed and wet habitats.ConclusionsOur study shows that sprouting from roots is quite common in temperate dicotyledonous herbs. Two components of RS – ability and vigour – should be considered separately in future studies. We would also like to focus more attention on RS in herbs from other regions as well as on external forces and internal mechanisms regulating evolution and the functions of RS in both disturbed and undisturbed habitats.     

Annuals sprouting adventitiously from the hypocotyl: their compensatory growth and implications for weed management

Habitats, disturbed severely at least once a year, are often dominated by annual plants, which avoid disturbance by means of a short life span and massive production of seeds. Contrary to perennials, they lack pools of reserve meristems on and storage carbon in below-ground organs necessary for vegetative regeneration after disturbance. However, some annuals are able to initiate a bud bank on the hypocotyl after loss of their shoot. In three experiments, we investigated how the timing of disturbance or population origin affects adventitious bud formation on the hypocotyl for regeneration and compensatory growth in some annual weeds.     

Resprouting after disturbance: an experimental study with short-lived monocarpic herbs

We experimentally demonstrated the ability of three short-lived monocarpic species to vegetatively regenerate (resprout) from roots after severe disturbance. We assessed the relationship between resprouting ability and (1) timing of injury with respect to life-cycle stage (reproductive vs. vegetative plant), life-history mode (annual vs. winter annual) and phenological stage (flowering vs. fruiting plant), (2) nutrient availability, and (3) disturbance severity (removal of all axillary buds Yes/No). In a chamber experiment with the annual or potentially winter annualRorippa palustris, all injured plants resprouted in all nutrient levels and day-length regimes (day-length regimes simulated conditions of an annual and a winter annual cohort). The number of adventitious buds on roots was positively affected only by injury. The extent of regeneration and amount of regenerated biomass were higher at high nutrient level and long-day regime.     

The effects of seed weight on growth and competitive ability of Rumex acetosella from two successional old-fields

Summary The effects of seed size on growth, biomass allocation and competitive ability of Rumex acetosella plants grown either individually or in competition were studied in two populations (6 months and 15 years old respectively) sampled from a postcultivation successional gradient. For plants grown individually there were highly significant effects of seed weight on growth after 43 days, with a higher relative growth rate (RGR) observed for plants raised from heavier seeds. However at the end of the experiment, seedlings developed from lighter seeds had a RGR 2 times greater than those from heavier seeds. Final biomass of the two types was not significantly different after 73 days of growth. When plants were grown individually, there were only slight differences between populations, but when grown in monocultures of 4 plants per pot, plants from the old population had higher root and leaf biomass per pot whereas those from the young population had a higher reproductive effort per pot. This suggests that a trade-off between allocation to sexual and vegetative reproduction occurs over successional time. In mixtures of light and heavy seeds, plants from light seeds were shorter, had fewer leaves and lower biomass than plants from heavy seeds, which were also taller and produced more dry matter than plants grown from heavy seeds in monoculture. The significant effects of seed weight and population on biomass parameters persisted unit the end of the experiment. Seedlings from heavy seeds were strong competitors: those from the young population grew better in the presence of neighbors than in monoculture and those from the late successional population suppressed the more the growth of their partners. Seedlings from light seeds were subordinate competitors. These results suggest that seedlings from seeds of different sizes benefit from contrasting ecological conditions and that selection acts on reproductive output along successional gradients.     

Local adaptation and phenotypic plasticity both occurred in <Emphasis Type="Italic">Wedelia trilobata</Emphasis> invasion across a tropical island

The role of the local adaptation and phenotypic plasticity of invasive species in their invasion of new environments has historically been a debatable issue, particularly at small spatial scales (e.g., different habitats within an island). We selected seven field sites across Hainan Island, Hainan Province, China, to investigate the role of local adaptation and/or phenotypic plasticity in the successful invasion of Wedelia trilobata by a field survey, molecular marker analysis, and common garden experiment. In the field survey, the clonal growth characteristics of W. trilobata showed significant differences among the seven sites, suggesting that the species was able to adapt to different environments. The mean phenotypic plasticity index of W. trilobata was higher than that of other invasive plant species (0.61 vs 0.48). The analysis of the inter-simple sequence repeat molecular markers of 420 individuals from the seven sites revealed a Shannon’s index that was similar to those of other invasive plants (0.29 vs 0.25). The nested analysis of the molecular variance in the genetic diversity of the population showed significant differences among the sites. In the common garden experiment, the growth characteristics of plants grown from the seven sites were significantly affected by light and density treatments but not by soil moisture. However, the responses of plants grown from different sites to light treatment varied. Plants from sunny sites had greater clonal traits than those from shady sites, indicating that local adaptation occurred in plant populations grown at some sites. Overall, our results implied that both phenotypic plasticity and local adaptation contributed to the successful invasion of W. trilobata across Hainan Island.     

Bark structure and mode of canopy regeneration in trees of Melia azedarach L.

Summary The bark texture of Melia azedarach L. changes from smooth to furrowed as trees age. In trees that were cut down, those with smooth bark sprouted below the cut from suppressed buds; trees with thick, furrowed bark sprouted at the edge of the cut surface from adventitious buds. The trees that had thin, furrowed bark sprouted mainly at the edge of the cut from adventitious buds, but sometimes also from suppressed buds in cracks. The relationship between sprouting pattern and tree architecture are discussed.