Seedling stage of two subalpineAbies species in distinction from sapling stage: A matter-economic analysis

A growth analytical study is made on the seedlings ofAbies mariesii Mast. andAbies veitchii Lindl. in the subalpine climaxAbies forests of the northern Yatsugatake Mountains, central Japan. Seedlings are distinguished from saplings by the absence of the fully expanded lateral branch system. The high dependence of assimilation on new needles characterizes the lives of seedlings. Leader shoots of seedlings, resembling not leader shoots but lateral branch shoots of saplings, have shoot characters adaptive for assimilation. Seedlings grow into saplings at 20 cm in height and 5 g in dry weight. The matter-economic analysis suggests the existence of a boundary growth rate below which an individual cannot maintain the needle amount requisite for its survival (called the critical growth rate) and that above which an individual can easily enter the sapling stage due to higher allocation of assimilate to roots and aged trunk stem (the capacity growth rate). Forest floor seedlings suffer, a high mortality during their initial several years and scarcely grow to enter the sapling stage, because of the scantiness of their matter production. In the regeneration patterns of subalpineAbies forests, both the seedling bank type and the sapling bank type are recognized.     

Differences in sapling architecture betweenFagus crenata andFagus japonica

The ecological significance of architectural patterns for saplings ofFagus crenata andFagus japonica co-occurring in a secondary oak forest were evaluated by comparing the size and shape of leaves, trunks and crowns.Fagus japonica saplings were different fromF. crenata saplings in some architectural properties: (i) the leaf area and specific leaf area were larger; (ii) the ratio of sapling height to trunk length was lower, indicating greater leaning of the trunk; and (iii) the projection area of the crown was larger and the leaf area index lower indicating less mutual shading of leaves. These architectural features indicated thatF. japonica saplings were more shade tolerant thanF. crenata andF. crenata saplings were superior toF. japonica for growth in height and could, therefore, utilize sunlight in the upper layer. An erect trunk inF. crenata and a leaning trunk inF. japonica may be important characteristics associated with the regenerations patterns of each species; regeneration from seedlings under canopy gaps in the former and vegetative regeneration by sprouting in the latter.     

辽东栎林内不同小生境下幼树植冠构型分析

以黄土高原黄龙山林区辽东栎林内3个小生境（林下、林隙、林缘）下辽东栎天然更新幼树为研究对象,采用典型抽样法对辽东栎幼树侧枝、叶片和树冠的空间分布状况以及生物量分配状况进行调查分析,探讨微生境与幼树植冠构型特征的关系,明确辽东栎幼树对不同小生境的适应策略,为栎林经营和林分结构优化提供理论依据。结果显示：（1）3种生境下辽东栎幼树构型发生了可塑性变化,林下幼树树冠层次比较单一,林隙与林缘的幼树树冠层次更加丰富。（2）由林下至林缘,幼树的树高、枝下高呈逐渐减小的趋势,而地径变化趋势与之相反;幼树的冠幅、树冠面积、树冠率呈先增加后减小的趋势,并且林下与林隙、林缘的差异显著;幼树的总体分枝率、逐步分枝率、枝径比呈先增加后减小的趋势。（3）3种生境下,幼树的一级枝的枝长、直径与倾角随着树高的增加而呈减小的趋势,但3种生境的差异不显著;林下一级枝主要分布在冠层中上部,而林隙与林缘一级枝主要分布在冠层中下、中上部。（4）由林下至林缘幼树叶长、叶宽、单叶面积和比叶面积逐渐降低,而单株叶数、叶总面积、叶面积指数呈先增大后减小趋势;与其他2种生境相比林下叶片分布趋于冠层上部。（5）幼树地上部分生物量中林下主干生物量占83%,枝和叶生物量只占17%;而林隙与林缘虽然各部位生物量有所差异但比例基本一致,其中主干占66%左右,枝和叶生物量占34%左右。研究表明,林隙生境下幼树的构型优于林缘和林下生境,在今后栎林的经营中,可以通过适当间伐来增加林隙数量,为森林更新和结构的优化提供有利条件。     

Convergent evolution of the lateral line system in Apogonidae (Teleostei: Percomorpha) determined from innervation

The lateral line system and its innervation were examined in two species of the family Apogonidae (Cercamia eremia [Apogoninae] and Pseudamia gelatinosa [Pseudamiinae]). Both species were characterized by numerous superficial neuromasts (SNs; total 2,717 in C. eremia; 9,650 in P. gelatinosa), including rows on the dorsal and ventral halves of the trunk, associated with one (in C. eremia) and three (in P. gelatinosa) reduced trunk canals. The pattern of SN innervation clearly demonstrated that the overall pattern of SN distribution had evolved convergently in the two species. In C. eremia, SN rows over the entire trunk were innervated by elongated branches of the dorsal longitudinal collector nerve (DLCN) anteriorly and lateral ramus posteriorly. In P. gelatinosa, the innervation pattern of the DLCN was mirrored on the ventral half of the trunk (ventral longitudinal collector nerve: VLCN). Elongated branches of the DLCN and VLCN innervated SN rows on the dorsal and ventral halves of the trunk, respectively. The reduced trunk canal(s) apparently had no direct relationship with the increase of SNs, because these branches originated deep to the lateral line scales, none innervating canal neuromast (CN) homologues on the surface of the scales. In P. gelatinosa, a CN (or an SN row: CN homologue) occurred on every other one of their small lateral line scales, while congeners (P. hayashii and P. zonata) had an SN row (CN homologue) on every one of their large lateral line scales.     

Allometry, root/shoot ratio and root architecture in understory saplings of deciduous dicotyledonous trees in central Japan

Plant allometry that is related to plant architecture and biomass allocation strongly influences a plants ability to grow in shaded forest understory. Some allometric traits can change with plant size. The present study compared crown and trunk allometries, root/shoot biomass allometry, and root architecture among understory saplings (0.25--5m height, except for two trees > 5 < 7 m) of seven deciduous dicotyledonous species in central Japan. Associations of the crown and trunk allometries with several plant morphological attributes were analyzed. Branch morphology (plagiotropyvs orthotropy) and life size were correlated with sapling crown and trunk allometries. Both large leaves and orthotropic branches were associated with a narrow small crown and slender trunk. The root/shoot ratio decreased rapidly with increasing plant height for saplings shorter than about 1.5 m. Less shade-tolerant species tended to have smaller root/shoot ratios for saplings taller than 1.5 m. With an increase in plant height, the branch/trunk biomass ratio decreased for saplings with plagiotropic branches but increased for saplings with orthotropic branches. Four subcanopy species (Acer distylum, Carpinus cordata, Fraxinus lanuginosa and Acanthopanax sciadophylloides) had superficial root systems; a common understory species (Sapium japonica) had a deep tap root system; and a canopy species (Magnolia obovata) and a subcanopy species (Acer tenuifolium) had heart root systems of intermediate depth. The root depth was not related to shade tolerance. Among species of the same height, the difference in fine root length can be 30-fold.     

微地形对江西武夷山南方铁杉针阔混交林幼树更新的影响

为探讨江西武夷山南方铁杉针阔混交林内不同微地形中幼树更新特征的差异,明晰不同微地形生境对幼树天然更新的影响。以江西武夷山国家级自然保护区内海拔约1800m的南方铁杉针阔混交原始林为研究对象,基于在其中建立的中亚热带南方铁杉针阔混交林动态监测固定样地首次调查数据,将固定样地中160个20m×20m的样方根据其海拔、凹凸度和坡度3种地形参数通过C-均值模糊聚类划分成不同的微地形生境,比较这不同微地形下的更新幼树种类组成及幼树更新特征,包括幼树密度,幼树平均胸径、平均高、平均冠幅,空间分布格局,分析不同微地形下幼树更新特征与地形因子、林分因子之间的关系。结果显示：(1)通过聚类分析,最终将固定样地的微地形生境划分成4类,分别为陡坡、凹地、凸地、缓坡。(2)4类微地形更新幼树优势种组成类似,但优势程度存在差异。闽皖八角幼树在4类微地形中的重要值皆为第一,均大于43%。建群种南方铁杉的幼树在凸地的重要值为9.09%,具有一定优势;在陡坡的重要值为0.62%,优势程度较差。(3)陡坡的更新幼树密度最高,为399株/hm~2,高于凹地,凸地和缓坡;幼树平均胸径和平均高的大小表现为：缓坡>凸地&...     

Carbon uptake and respiration in above-ground parts of a Larix decidua × leptolepis tree

Summary Shade needles of hybrid larch (Larix decidua × leptolepis) had the same rates of photosynthesis as sun needles per dry weight and nitrogen, and a similar leaf conductance under conditions of light saturation at ambient CO₂ (A_max). However, on an area basis, A_max and specific leaf weight were lower in shade than in sun needles. Stomata of sun needles limited CO₂ uptake at light saturation by about 20%, but under natural conditions of light in the shade crown, shade needles operated in a range of saturating internal CO₂ without stomatal limitation of CO₂ uptake. In both needle types, stomata responded similarly to changes in light, but shade needles were more sensitive to changes in vapor pressure deficit than sun needles. Despite a high photosynthetic capacity, the ambient light conditions reduced the mean daily (in summer) and annual carbon gain of shade needles to less than 50% of that in sun needles. In sun needles, the transpiration per carbon gain was about 220 mol mol^–1 on an annual basis. The carbon budget of branches was determined from the photosynthetic rate, the needle biomass and respiration, the latter of which was (per growth and on a carbon basis) 1.6 mol mol^–1 year^–1 in branch and stem wood. In shade branches carbon gains exceeded carbon costs (growth + respiration) by only a factor of 1.6 compared with 3.5 in sun branches. The carbon balance of sun branches was 5 times higher per needle biomass of a branch or 9 times higher on a branch length basis than shade branches. The shade foliage (including the shaded near-stem sun foliage) only contributed approximately 23% to the total annual carbon gain of the tree.     

Early spring leaf out enhances growth and survival of saplings in a temperate deciduous forest

Saplings of many canopy tree species in winter deciduous forests receive the major portion of their light budget for their growing season prior to canopy closure in the spring. This period of high light may be critical for achieving a positive carbon (C) gain, thus contributing strongly to their growth and survival. This study of saplings of Aesculus glabra and Acer saccharum in Trelease Woods, Illinois, USA, tested this hypothesis experimentally by placing tents of shade cloth over saplings during their spring period of high light prior to canopy closure in three consecutive years. Leaf senescence began 16 days (year 0) and 60 days (year 1) earlier for shaded A. glabra saplings than control saplings. No change in senescence occurred for A. saccharum. The annual absolute growth in stem diameter of both species was negligible or negative for shaded saplings, but positive for control saplings. Only 7% of the shaded A. glabra saplings were alive after 2 years, while all control saplings survived for 3 years; only 20% of the shaded A. saccharum saplings survived for 3 years, while 73% of control saplings were alive after the same period. Early spring leaf out is a critical mechanism that allows the long-term persistence of saplings of these species in this winter deciduous forest. Studies and models of C gain, growth, and survival of saplings in deciduous forests may need to take into account their spring phenology because saplings of many species are actually “sun” individuals in the spring prior to their longer period in the summer shade.     

Can saliva from moose,Alces alces,affect growth responses in the sallow,Salix caprea?

Herbivores have the potential to affect the morphological traits of the plants they feed on, such as the breaking of apical dominance that occurs when shoot tips are browsed, leading to increased lateral branching and decreased competition among growing points. Despite such effects, however, it remains unclear whether components in the saliva of the browsing animals are directly involved in amplifying and/or reducing the plant growth responses. To test this possibility, a controlled experiment was performed in which herbivory by moose ( Alces alces ) was simulated by tearing 60 sallow saplings ( Salix caprea ) with a moose jaw. Of these 60, half were also treated with moose saliva. Selected growth traits of the torn plants with and without saliva treatment were examined directly after treatment (week 0) and 1, 2, 4, 6, 8, 10, 12 and 15 weeks after the tearing. Also included in the study was an untreated (no tearing, no saliva) control group of another 30 sallow saplings. Traits monitored on the saplings were height and the number of branches, buds and leaves. Application of moose saliva on torn saplings led to significantly more branches than on saplings without saliva treatment. Moose saliva, however, had no significant effects on the other growth traits, although for most of these characteristics both groups of torn saplings showed increased values compared to the undamaged control. Overall, these results demonstrate that moose saliva has a consistent stimulatory effect on branching of sallow saplings but not on the other growth traits examined in this study.     

Fungal succession on pine needles in Germany

The mycofloral succession on the needles ofPinus sylvestris was investigated in Tübingen, southwest Germany. Dead needles attached to the branches (D-type), those caught on branches (C-type) and three types of fallen needles, i.e., freshly fallen (L-type), slightly discolored (OL-type) and almost black needles (F-type) were examined for their fungal flora. Common primary saprophytes were rich on the dead needles on the tree, and on the L-type needles. They were replaced by successive species that contained the well-known species preferring pine needles as their substratum, such asVerticicladium trifidum orSympodiella acicola. Their ecological niches in pine leaf litter and their distribution patterns from a biogeographical viewpoint were discussed.     

Influence of needle loss,yellowing and mineral content on monoterpenes in the needles of Picea abies (L.) Karst.

Summary Monoterpenes in needles of Picea abies (L.) Karst. were studied to reveal whether or not the symptoms of forest decline observed in three mountain regions of South Germany (Bavaria) — needle loss and needle yellowing — are related to changes in the amounts of all or individual terpenes. The nutrient supply of the needles was examined in addition to the terpene concentrations, since the disease symptom montane yellowing is often associated with mineral deficiency. At two of the eight locations, trees exhibited Mg-deficiency, at one location K-deficiency was observed, and at another location the S-content of the needles indicated SO₂-pollution. Using various statistical methods of analysis, no correlation was observed between the mineral element content of the needles, the percentage of needle loss and either the absolute or percentile terpene amounts stored within the needles. This finding is independent of needle age, date of sampling and terpene pattern. Concerning needle yellowing, the data show a tendency towards a reduction of the terpene concentrations in needles originating from branches with partly yellow needles compared to needles from exclusively green-needled branches. In spite of the fact that only 2-year-old and older needles show the disease symptom of yellowing, the terpene level is reduced even in still green, juvenile and 1-year-old needles. No terpene was found to be an indicator for early recognition of injury.     

Photosynthetic capacity,chloroplast pigments,and mineral content of the previous year's spruce needles with and without the new flush: analysis of the forest-decline phenomenon of needle bleaching

Summary Spruce (Picea abies) damage in the Fichtelgebirge (FRG) occurs as needle bleaching and a depression of CO₂ assimilation. Such injury may primarily result from the direct, above-ground effects of air pollution or indirect, below-ground changes in mineral uptake.Typically, the new flush of spruce needles is green and exhibits high photosynthetic capacity. Mies and Zöttl concluded that the older foliage is damaged when nutrients are withdrawn to supply the current year's needles. By removing the terminal buds of single branches in the spring, we produced an experimental set of the previous year's needles with greater mineral reserves than the control needles. During the course of the growing period, the performance of the experimental needles, which lacked competition from the new flush, was compared to that of the control needles of the same age-class on intact branches with the new flush.Throughout the experiment, chloroplast pigments of a healthy control tree were not affected by the elimination of the new flush. However, the chlorophyll and carotenoid content as well as the photosynthetic capacity of the previous year's needles on those branches of a heavily damaged tree where the new flush had been eliminated increased substantially. This increase was associated with an increase in minerals, which seemed to be deficient in the control needles with the new flush. Thus, in contrast to needles of the same age-class on intact branches with undisturbed new growth in the same atmospheric environment, the experimental needles escaped bleaching and a decrease in photosynthesis. It would seem that the bleaching and the loss in photosynthetic capacity typical of trees damaged by forest decline indirectly result from nutrient deficiencies through soil environment changes and/or root damage than directly from atmospheric pollutants.     

不同光环境下紫椴幼树树冠结构的可塑性响应

从冠形、侧枝和叶片在树冠中的空间分布角度对天然更新紫椴幼树的树冠结构进行了论述,认为紫椴幼树树冠对光照条件的变化有显著的可塑性响应.强光通过抑制主干的生长促进了侧枝的分化,庇荫则通过抑制1级侧枝的生长促进了侧枝的再分枝.随着光照水平的降低,紫椴幼树的数量叶片密度显著降低,且叶片逐渐集中于冠上层.林冠下的紫椴幼树通过这种侧枝和叶片的分布格局,在形态上提高其对光的截获能力在适度庇荫环境中,紫椴幼树垂直生长采取演替先锋种的"避荫”对策,侧枝生长采取中等耐荫种的"掠光”对策;在弱光环境中,紫椴幼树则采取典型的忍耐适应行为.这种树冠结构的变化是提高紫椴幼树对光的截获能力的一种有益适应.     

Performance of pine looper Bupalus piniarius larvae under population build-up conditions

In the first year of an outbreak, Bupalus piniarius larvae, encounter intense crowding. In the later stages of larval development, they are forced to feed on the non-preferred current-year needles of Scots pine or even on alternative hosts. It was hypothesized that larval feeding on a non-preferred resource (current-year needles) will negatively affect B. piniarius performance. It was also hypothesized that larval mutual interference (crowding without competition for food) will have negative additive effects. These hypotheses were tested in laboratory and field experiments. Fourth instar larvae were reared singly and under crowded conditions in cohorts of ten. Larvae in both situations were reared on control branches (containing both mature and current-year shoots) and branches containing only current-year shoots. Crowded larvae were reared also on Norway spruce, an alternative host. Crowding and feeding on a non-preferred resource had opposite effects on B. piniarius larval performance. Crowding in the late larval instars enhanced larval performance while absence of the preferred resource had negative effects. Larval growth rate was higher and development time was shorter for larvae exposed to crowded conditions than for solitary larvae. There was, however, no difference between the groups in final pupal weights or survival. Survival was 25% lower for larvae feeding on non-preferred current-year needles and pupal weights 9% lower, compared with results for larvae feeding on mature needles. Larvae feeding on Norway spruce suffered greatly extended development time, 82% lower survival, and resulted in 60% lighter pupae compared with conspecifics on Scots pine. It was concluded that not only quantity but also quality of the available food resource is critical for B. piniarius development.     

沙地樟子松天然林南缘分布区林木竞争、空间格局及其更新特征

以呼伦贝尔沙地樟子松地理分布南缘天然林为研究对象,采用Hegyi竞争指数与点格局等分析方法,研究了沙地樟子松天然林的种群结构、种内竞争、空间格局及幼树更新等特征。结果表明:1)所调查区域天然沙地樟子松纯林处于中幼龄阶段,属增长型种群;2)其竞争指数与对象木胸径服从幂函数关系CI=242.24D~(-1.12)(R~2=0.91);3)幼树在小尺度上呈聚集分布,中树与大树在中大尺度上呈随机分布;幼树与中树在小尺度上呈正相关性,中树与大树在小尺度呈负相关性;4)竞争指数与更新幼树和存活更新幼树的密度均呈显著正相关性。在林分管理中需要充分考虑林木竞争、空间格局以及种群更新的关系,本研究可为沙地樟子松天然林的经营管理与保护提供重要的科学依据。     

Ungulate browsing in winter reduces the growth of <Emphasis Type="Italic">Fraxinus</Emphasis> and <Emphasis Type="Italic">Acer</Emphasis> saplings in subsequent unbrowsed years

Browsing by ungulates has become a hotly debated issue in many European mountain forests in the past century. Acer pseudoplatanus L. and Fraxinus excelsior L. are broadleaved tree species that are preferentially browsed by roe deer (Capreolus capreolus) in central Europe. We analyzed growth data from shaded saplings of both tree species to quantify the extent to which height growth after game browsing is reduced in subsequent, unbrowsed years in forest stands. Sixty saplings of F. excelsior and A. pseudoplatanus from forest stands at Albisriederberg (Switzerland) were available to us that had been dissected into pieces that then were split in the middle for counting tree rings and assessing ungulate damage. We fitted the von Bertalanffy growth equation to these height growth data and included a reduction factor for winter browsing. Both tree species showed significantly reduced height growth in unbrowsed years after one to several browsing events in winter, and this effect increased with the number of browsing events. Saplings with a high growth rate showed a higher growth reduction. After winter browsing, height growth of A. pseudoplatanus saplings was less affected in unbrowsed years than that of F. excelsior saplings. We conclude that browsed saplings of these species in forest stands are not able to compensate browsing-induced height loss, but that height differences between browsed and unbrowsed saplings probably increase over time. A comparison between our analysis and the parameters estimated using equations published by Eiberle for predicting age at 130 cm height suggests that our parameter values are rather conservative estimates of the growth reduction effect after winter browsing. Neither F. excelsior nor A. pseudoplatanus show a distinct pattern in browsing-induced growth reduction with respect to soil moisture, nutrient level, and altitude. We thus conclude that our results are likely to be valid for a wide range of forested sites.     

Positive and negative effects of grass,cattle, and wild herbivores on <Emphasis Type="Italic">Acacia</Emphasis> saplings in an East African savanna

Plant–plant interactions can be a complex mixture of positive and negative interactions, with the net outcome depending on abiotic and community contexts. In savanna systems, the effects of large herbivores on tree–grass interactions have rarely been studied experimentally, though these herbivores are major players in these systems. In African savannas, trees often become more abundant under heavy cattle grazing but less abundant in wildlife preserves. Woody encroachment where cattle have replaced wild herbivores may be caused by a shift in the competitive balance between trees and grasses. Here we report the results of an experiment designed to quantify the positive, negative, and net effects of grasses, wild herbivores, and cattle on Acacia saplings in a Kenyan savanna. Acacia drepanolobium saplings under four long-term herbivore regimes (wild herbivores, cattle, cattle + wild herbivores, and no large herbivores) were cleared of surrounding grass or left with the surrounding grass intact. After two years, grass-removal saplings exhibited 86% more browse damage than control saplings, suggesting that grass benefited saplings by protecting them from herbivory. However, the negative effect of grass on saplings was far greater; grass-removal trees accrued more than twice the total stem length of control trees. Where wild herbivores were present, saplings were browsed more and produced more new stem growth. Thus, the net effect of wild herbivores was positive, possibly due to the indirect effects of lower competitor tree density in areas accessible to elephants. Additionally, colonization of saplings by symbiotic ants tracked growth patterns, and colonized saplings experienced lower rates of browse damage. These results suggest that savanna tree growth and woody encroachment cannot be predicted by grass cover or herbivore type alone. Rather, tree growth appears to depend on a variety of factors that may be acting together or antagonistically at different stages of the tree’s life cycle.     

Monophyletic origin of the dorsally arched lateral line in Teleostei: evidence from nerve innervation patterns

Branching patterns of the horizontal septum lateral line nerves (HSN) were studied in 123 teleostean species (including literature records) assigned to 96 families in 28 orders, primarily to indentify the group characterized by the presence of the dorsal longitudinal collector nerve (DLCN) for innervation of the trunk lateral line. In nonacanthomorphs, DLCN was absent, the trunk lateral line being mostly innervated by branches directly detached from HSN or those derived from the collector nerve running parallel to the former. In acanthomorphs, the dorsally arched trunk lateral line, typical of the group, was uniformly innervated by DLCN, indicating that presence of the latter was a synapomorphy of the group. Within the latter, DLCN was absent in Gasterosteiformes (Fistularia and Macroramphosus), Mugilidae, Atherinomorpha, Champsodontidae, Blenniidae, Callionymidae, Gobioidei, Istiophoridae, Gempylidae, Cynoglossidae, Ostraciidae, and Molidae. Monophyly of the Mugilidae plus Atherinomorpha was discussed based on the specialized innervation pattern.     

赤泥掺拌马尾松叶对芦竹与翠芦莉生长的影响

赤泥是铝土矿提炼氧化铝后排放的强碱性废渣,数量巨大且环境风险大,如何改良及筛选适生植物是其生态修复的关键。该研究通过掺拌不同比例的马尾松叶2%,4%,6%(w/w),分析其对赤泥pH与有机质含量及芦竹与翠芦莉生长的影响。结果表明:掺拌马尾松叶35 d后,赤泥pH由11.08显著下降至9.70,但随后趋于平稳;随着掺拌比例的增加,赤泥pH呈下降趋势,有机质含量由6.13 g·kg~(-1)显著增至17.52 g·kg~(-1)。芦竹与翠芦莉在纯赤泥上生长2个多月后死亡,但在掺拌4%马尾松叶的赤泥上均能较好地生长。其中,芦竹的生物量及相对生长速率(RGR)与栽培土相比不受影响,但地下/地上生物量比(B/A)显著增加;相反,翠芦莉的生物量和相对生长速率与栽培土相比显著降低,但B/A不受影响。     

Skeletal development in <Emphasis Type="Italic">Acropora palmata</Emphasis> (Lamarck 1816): a scanning electron microscope (SEM) comparison demonstrating similar mechanisms of skeletal extension in axial versus encrusting growth

Many Acropora palmata colonies consist of an encrusting basal portion and erect branches. Linear growth of the skeleton results in extension along the substrate (encrusting growth), lengthening of branches (axial growth) and thickening of branches and crust (radial growth). Scanning Electron Microscopy is used to compare the mechanisms of skeletal extension between encrusting growth and axial growth. In encrusting growth, the distal margin of the skeleton lacks corallites (which develop about 1 mm from the edge); in contrast, in axial growth, axial corallites along the branch tip form the distal portion of the skeleton. In both locations, the distal margin of the skeleton consists of a lattice-like structure composed of rods that extend from the body of the skeleton and bars that connect these rods. An actively extending skeleton is characterized by sharply pointed rods and partially developed bars. Distal growth of rods (and formation of bars) is effected by the formation of new sclerodermites. Each sclerodermite begins with the deposition of fusiform crystals (that range in length from 1 to 5 μm). These provide a surface for nucleation and growth of spherulitic tufts, clusters of short (<1 μm long) aragonite needles. The needles that are oriented perpendicular to the axis of the skeletal element (rod or bar), and perpendicular to the overlying calicoblastic epithelium, continue extension to appear on the surface of the skeleton as 10–15 μm wide bundles (of needle tips) called fasciculi. However, some crusts that abut competitors for space have a different morphology of skeletal elements (rods and bars). The distal edge of these crusts terminates in blunt coalescing rods, and bars that are fully formed. Absence of fusiform crystals, lack of sharply pointed rods and bars, and full development of sclerodermites characterize a skeletal region that has ceased, perhaps only temporarily, skeletal extension.