"Chinese Banyan grows Aerial roots of ‘rapidly with but little care, its Ficus microcarpa foliage is of a glossy green Mathew Pryor and Li Wei colour, and it soon affords an agreeable shade from the fierce rays of the sun, which renders it particularly valuable in a place like Hong-kong’."
Robert Fortune, (1852). A Journey to the Tea Countries of China
Section of flexible aerial root of Ficus microcarpa
This article reports on a study to The distribution and growth of aerial since the beginning of the colonial investigate the nature of aerial roots in roots was observed to be highly variable, period,2 and was used almost exclusively Chinese banyan trees, Ficus microcarpa, but there was a clear link between for this purpose until the 1870s.3 The and the common belief that their growth and high levels of atmospheric botanist Robert Fortune noted, as early presence and growth is associated with humidity. The anatomical structure of as 1852,4 that the Banyan grew ‘rapidly wet atmospheric conditions. the aerial roots suggests that while with but little care, its foliage is of a aerial roots could absorb water under glossy green colour, and it soon affords First, the form and distribution of free- certain conditions, their growth was an agreeable shade from the fierce rays hanging aerial roots on eight selected generated from water drawn from of the sun, which renders it particularly Ficus microcarpa trees growing in a terrestrial roots via trunk and branches, valuable in a place like Hong-kong’. public space in Hong Kong, were mapped and that the association with humid Even the Hongkong Governor, in 1881, on their form and distribution. Secondly conditions was most likely to be due to observed that Banyans turned ‘glaring the extension of selected sample aerial the greater availability of ground water roads to green avenues with the rapidity roots from each tree were measured in such conditions. that would surprise arboriculturists in over twelve months against prevailing Europe’.5 atmospheric humidity. Lastly, section Introduction samples of aerial roots of different It has been valued both for its shade and ages were taken, and the anatomical Chinese Banyan, Ficus microcarpa, is a greenery, and its ability to cope with the structure was observed and compared native of Southern China and has been typhoon winds and the poor growing with that of terrestrial water-absorbing planted as a shade tree throughout environment in dense urban settings. roots to assess the mechanism by which the region for centuries. In Hong Kong, The majority of Hong Kong’s wall trees they might take up water. it has been planted as a roadside tree are F. microcarpa,6 and it is the species
Yuan Lin 2015 Planting Futures / 77 that has been successfully transplanted the trunk or stem first as surface roots, to environmental conditions. Although aerial roots at different developmental most often at mature size within the and after they lignify may fuse with the aerial roots have been observed to stages, and their potential for Territory7. stem, creating highly complex surface absorb water under certain conditions,17 absorbing water from the atmosphere. rooting structures. the mechanism by which they do so has ‘Banyan’ is a generalized term used to not been investigated, and how this From these, an understanding of the refer to Ficus trees of the Urostigma Gill separately defines “clasping” aerial might affect the growth of the aerial root nature of aerial roots and their role in the subgenus of Moraceae, which includes roots that are exposed, but remain has not been assessed. growth of the tree can be formed, which tree species with aerial adventitious appressed to some surface, as seen in may help explain the predominance of roots.8 A number of these grow in Hong the root fan of a wall tree. Aerial roots The objectives of this research study were Chinese banyans in manmade landscapes Kong, e.g. F. microcarpa, F. benjamina, F. can also develop from the callus tissue to understand the role of flexible aerial in Hong Kong. benghalensis, F. elastica, F. macrophylla, around a bark injury which has severed roots in the growth and development of and F. altissima.9 the phloem,15 and have been observed mature Chinese Banyan trees in Hong Materials and methods to bridge over sizeable trunk wounds Kong. Specifically, to investigate: The origin of aerial roots of Ficus trees has (spanning > 500mm), ultimately closing Eight mature Ficus microcarpa trees not been studied in detail. In Southern the wound altogether.16 • the occurrence of aerial roots within were selected for the study by random China, it is widely believed that the the tree, i.e. their number and broad number from a set of 52 trees growing in growth of aerial roots of Chinese Banyan Currently there has been no systematic distribution within the structure of the paved areas in public spaces in Lei King is related to periods of high atmospheric study of the conditions under which tree, Wan, Eastern District. They had all been humidity. Aerial root development flexible aerial roots occur on mature • the development and elongation rate planted at approximately the same time is seasonal with the initiation and Chinese banyan trees, their presence of aerial roots, in relation to and were some 30 years old. The trees elongation of roots starting in spring and distribution within the tree, their environmental conditions, were healthy and vigorous, and growing with the rise in atmospheric temperature growth rates, and how these might relate • the morphological structure of the in identical environmental conditions. and humidity, and continuing until late They ranged from 9.0 to 12.0m in height, autumn when humidity falls again.10 with trunk diameters of 0.24-0.55m From this, it has been assumed that (DBH), and average canopy spread of 9.0- aerial roots are able to absorb water and 13.0m. Landscape maintenance workers nutrients from the atmosphere to sustain reported that free-hanging roots were their growth. However, little research periodically cut (typically twice a year) has been conducted on this point. at approx. 2.0m above the ground, to prevent them from reaching the ground, Gill (1975) notes that adult F. microcarpa and to avoid nuisance to park users. trees produce slender, pendulous (free- hanging) aerial roots, i.e. roots exposed First, the distribution of aerial roots to air for at least of 50% each day and within each tree was mapped. As no free of any support or substrate,11 which methodology for mapping aerial roots under gravity grow downward. There is has previously been established, the a high degree of variability between tree following was devised for this study. specimens in the number of aerial roots The point of origin for each cluster of Typical pattern of aerial roots on a mature Chinese Banyan and their distribution within the canopy, free-hanging aerial roots was identified but no clear indication of what factors and its distance from the centre of the flexible aerial will thicken into a lignified take several years to reach the ground influence this variability. tree was measured. The diameter of the aerial within one to three years. The or come into contact other stems or stem at the point of origin was noted, lignified aerial root has a similar structures. Zimmermann, et al. (1968) From simple field observations, there are together with its position within the appearance to a branch but does not describe the process of lignification three distinct stages in the development cross section of the stem (stems divided bear foliage. of aerial roots in Ficus benjamina,13 of aerial roots. into sectional quarters). The biomass a closely related species. When the of each cluster was calculated as the Aerial roots originate from a single point flexible aerial root reaches soil it initiates 1. Growing tip – 1.5-2.0mm diameter, up product of the aggregate diameter of on a branch or stem, and as they grow and elongates terrestrial roots to absorb to 120mm long, pale yellow, flexible aerial roots within the cluster and their they divide at the tip. Mature roots may water and nutrients. This new terrestrial but brittle, average length (measured at the start of have all three stages present, with a root system forms an anchor, allowing 2. Flexible aerial root – 2.0-5.0mm the study). Results for the percentage of single lignified root giving rise to a cluster the above ground portion of the root diameter, up to 10.0m long, dark total aerial root biomass for the tree by: of many (can be <50 no.) individual to contract and straighten by producing reddish-brown, woody, flexible, (a) distance from the centre of the tree; flexible aerial roots and growing tips. tension wood. Finally, the root enters 3. Lignified aerial root – >5.0mm (can be (b) stem size; and (c) position of point of The cluster is a self-contained system a consolidation phase, thickening to >100mm) woody, light grey, rigid. origin on the stem, are given in Table 1. within which individual flexible aerial become prop stem to support lateral roots can intertwine, but do not fuse branches.14 Prop stems are noticeably In all three stages the longitudinal form Second, the rate of elongation of roots together. straighter than lignified aerial roots that of the root is variable from straight to was measured in relation to atmospheric have not reached the ground. very twisted, although they appear to humidity. Selected sample roots from Roots elongate very rapidly, and have become more twisted with the age. The each tree were tagged, and a reference been observed in a Miami based study to Aerial roots produced from branches growing tip will mature into a flexible point was identified on the root (typically lengthen by up to 10mm per day.12 Aerial immediately around the main trunk or aerial within two to three weeks. The Mature Ficus microcarpa trees growing in a paved publlic space the lowest branching junction). The roots arising in the upper canopy can mature stems, may attach themselves to in Lei King Wan, HK
78 / Yuan Lin 2015 Planting Futures Yuan Lin 2015 Planting Futures / 79 Aerial root growth Anatomical structure The mature flexible aerial root, in section (Fig. 2), shows many xylem vessels. Aerial roots selected for measurement The new aerial root tip, in section (Fig. Medullary rays cross the xylem. The were all active. They started elongating 1), shows one layer of exodermis cells broad cortex has been sloughed off and in late February and stopped sometime in covering a broad cortex, consisting the parenchymatous pith has become October. Rate of root elongation varied of 9-12 layers of parenchyma cells, lignified. Lenticels are raised. The radial over the course of the year, with April arranged closely. The endodermis is not longitudinal sections through the mature to August being the most active months well defined. The roots have 4-5 xylem aerial root (Figs. 5 and 6), indicate more (Table 2). There was little or no growth groups. A broad parenchymatous pith xylem vessels and some scattered between November and February. In occupies the centre. sclereids. averaged measurements across samples from all eight trees, root elongation was The radial longitudinal section through Discussion greatest in May, with an average monthly the new aerial root tip (Fig. 3), shows increase 244.9mm. Roots extended on three distinct regions: division zone, The distribution of aerial roots was average by 1154.3mm over the year. elongation zone and differentiation zone, highly variable. Some trees had very few as would be expected in a terrestrial root or no aerial roots at all, while immediate Individually the rate of elongation of structure. But the root tip has no root neighbours (in the same environmental flexible aerial roots varied very greatly hairs in the differentiation zone. In the conditions), might have many hundreds. between different roots. One root elongation zone, roots begin secondary Although the trees were of the same might elongate only a few millimeters in growth. In detailed section (Fig. 4), age, their size (reflecting past growth) a month while its immediate neighbor the cork cambium differentiates cork was very different. No relationship length of the root below the reference the densest pattern of aerial roots, had a from the centre. The majority (76.5%) within the same cluster might put on a outwards and phelloderm inwards. The was observed between size of tree and point was measured every week over a biomass of 38.5 ltrs. The radial distance was found on stems between 100 and few hundreds of millimeters of growth. epidermis, as the outmost cell layer, presence of aerial roots. Small trunk period of twelve months. The difference of the point of origin of the roots from 250mm diameter. Only one tree had The maximum elongation of any single could be shed as the tree grows and diameter trees were as likely to have between successive measurements the centre of the tree was categorized roots on a stem >250mm, but only three root (from all samples) in one day was includes many lenticels. Most lenticels aerial roots, (and the same volume of represented the elongation over the time into 1.0m intervals. The tree canopy of the trees had branches of this size. 17.4 mm, (321.8mm in one month on the epidermis are transversely aerial roots) as large trunk diameter interval. Records of the mean weekly spread (expressed as a radius) varied Only a few roots were found on small 1983.4mm across the year) orientated. trees. atmospheric temperature and relative between 4.5m and 6.5m, although diameter stems (0-50mm), although humidity for the period were obtained with the close arrangement of trees, on one tree these accounted for more from the Hong Kong Observatory. canopies tended to be elongated along than 10% of the total. Aerial roots were one axis. Nearly two thirds (62.3%) of predominantly (85.8%) growing from the Lastly, specimens of flexible aerial the aerial root biomass was within 2.0m underside of stems, with only a small roots were collected from two of the of the trunk which broadly reflects the percentage growing from the two sides trees. Samples were taken from both proportion of the branch biomass within of the stem, and very few (1.7%) from the tip and the central portions of the this distance of the trunk. 12.6% of the the top side. aerial roots. These were cut into 10mm aerial root biomass was beyond 4.0m sections and fixed in FAA (Formalin- Acetic Acid - Alcohol) for at least 24 Low High Average hours. Sections were embedded in paraffin after dehydration, then cut Number of aerial root clusters (no.) 1 44 13.7 with 8-10μm on a rotary microtome, Fig. 1. Section of aerial root tip of Ficus Fig. 2. Section of flexible aerial root Fig. 3. Radial longitudinal section of Total aerial root biomass (ltrs) and finally stained with safranin and 0.025 38.5 12.6 microcarpa. X10. 1. Exodermis, 2. of Ficus microcarpa. X10. Cortex has an aerial root tip of Ficus microcarpa, Cortex, 3. Endodermis, 4. Xylem, and been slough off. 1. Xylem vessels 2. (x5). 1. Root cap; 2. Cortex; 3. fast green. The sections were observed Distance from the trunk (m) Proportion of aerial root biomass 5. Broad pith. Medullary ray 3. Pith Xylem; 4. Pith; 5. Division zone; and 6. 0-1.0m 0% 66.0% 37.6% under a light microscope and photos Elongation zone taken with Motic Images Advanced 3.2 1.0-2.0m 21.8% 100.0% 24.7% software. The anatomical structure was 2.0-3.0m 0% 28.8% 15.3% 3.0-4.0m 0% 18.4% 9.9% observed and analyzed to determine the 4.0-5.0m 0% 12.1% 7.5% ability of the different portions of the 5.0-6.0m 0% 8.6% 5.1% aerial roots to absorb water. Stem diameter (mm) Proportion of aerial roots 0-50mm 0% 10.2% 3.8% Results 50-100mm 0% 25.1% 12.4% 100-150mm 7.6% 100.0% 17.6% Distribution of aerial roots 150-200mm 0% 59.8% 28.4% 200-250mm 0% 49.6% 30.5% Amongst the eight trees, the number 250-300mm 0% 19.1% 7.3% of root clusters varied considerably Position on the stem cross section Proportion of aerial roots between the trees (from 1 to 44), with underside 76.9% 95.5% 85.8% Fig. 4. Detailed radial longitudinal Figs. 5 & 6. Detailed radial longitudinal section of a flexible aerial root of Ficus an average of 13.7 clusters per tree. The side 4.5% 19.2% 12.3% section of an aerial root of Ficus microcarpa, (two samples, x10). More xylem vessels exist in mature part of aerial aerial root biomass also varied. The tree top 0% 4.4% 1.7% microcarpa, (x10). 1. Epidermis; 2. root. 1. Xylem vessel; and 2. Sclereids. with just one small cluster measured at Cork; 3. Cork cambium; and 4. just 0.025 ltrs, while the largest tree with Table 1. Distribution and position of aerial roots of Ficus microcarpa Phelloderm
80 / Yuan Lin 2015 Planting Futures Yuan Lin 2015 Planting Futures / 81 The distribution of aerial root biomass the dry winter months. Rate of growth in roots and fine <2mm water absorbing Species Ficus microcarpa Ficus benghalensis (after Kapil and Rustagi 1966) within the canopy appeared to follow individual roots was inconsistent. Some terrestrial roots of F. benghalensis as the distribution of branch and twig grew steadily throughout the summer, described by Kapil and Rustagi18 (Table Character Aerial root (new) Aerial root (mature) Aerial root (new) Aerial root (mature) Terrestrial biomass within the canopy, with the others would grow quickly then stop. 2). The aerial roots of the two species absorbing root greatest proportion being close to the Averaged maximum daily extensions are fundamentally alike, and both have Root Hair Absent Absent Absent Absent Present trunk. Broadly, the distribution of aerial for the five months June, July, August, distinct pith but lack of root hairs. These Cortex 9-12 cells thick Sloughed off 20-25 cells thick Sloughed off 8-15 cells thick roots around the canopy was even, i.e. Aril, and May ranged between 10.1 and two characteristics make them more Endodermis Poorly defined Poorly defined Poorly defined Poorly defined Better defined roots did not tend to grow just on one 12.4. This is in line with measurements resemblance to stem than terrestrial side. recorded in the Miami study. roots. Kapil and Rustagi also note Xylem strands 4-5 groups Absent Usually 5-7, Absent Usually 3 or 4, that the structure of aerial roots of F. occasionally 10-15 rarely up to 7 Aerial roots were observed to originate With an average annual elongation benghalensis has greater resemblance from all sizes of branch, some as small as of 1154.3mm, the vertical distance to stems. More vessels exist in Pith Distinct and board Lignified Distinct and large Lignified Absent or scanty 25mm diameter. A higher proportion of from the upper canopy to the ground, secondary xylem in F. microcarpa than F. aerial root biomass were growing from equated to several years growth. The benghalensis. Secondary Absent Less of Absent Many fibres, less Few fibres, more vascular parenchyma, of parenchyma, of parenchyma, larger diameter branches, compared to rougher bark of the flexible roots, with tissues many vessels, fewer and smaller numerous and smaller branches, but this was probably raised lenticels, served to prevent them Root hairs, however, are just structures well developed vessels, poorly large vessels, because of their relative age. from fusing together (as was observed in that substantially increase the absorbing medullary rays developed well developed the lignified aerial roots), allowing their surface of the roots, and the absence of medullary rays medullary rays Aerial roots were initiated, very largely, free movement during this time. root hairs would not prevent aerial roots Periderm Well developed Well developed Well developed Well developed Poorly developed from the underside of branches. This from absorbing water. As Esau notes, Lenticels Many Many Many, raised, Many Scanty, scattered is likely to reflect the more humid It was noted that where a root tip hairless epidermal cells are capable of transversely conditions there, compared to the upper stopped growing and had matured into absorbing water.19 oriented side, with rain water naturally draining to a flexible aerial root structure, further the lower side, and it being less exposure growth tended to be initiated through In terrestrial absorbing roots, water Table 3. Characteristics of aerial roots of Ficus microcarpa and Ficus benghalensis to sunlight. The fact that a few roots side shoot rather than extension of the passes from the absorbing cells to the initiated on the sides and upper surfaces existing root i.e. roots divided (ramified) conducting tissues. Esau identifies that in the same way as terrestrial roots. flexible aerial roots of F. microcarpa CO2 intake was reduced but they could of branches suggests that initiation is hence the multiple roots were usually the notable features of this pathway are: might act in a similar way, allowing absorb water like a sponge/activated not related to whether the wood is in found in clusters. Further, it was noted the presence of abundant intercellular In mature aerial roots of F. microcarpa, uptake water and movement to the carbon in at least 75% relative humidity compression or tension. that aerial roots grew by elongation spaces in the cortex but the lack of such existing vessels serve as conduits. Water conducting vessels. conditions. rather than by thickening, possibly to spaces in the vascular cylinder; together is actually drawn up from roots and The pattern of growth in aerial roots enable them to reach the ground as with the presence of a specialized transported to branches and leaves In terrestrial roots of dicotyledonous Conclusion was also highly variable, with some quickly as possible, while minimizing endodermis between the cortex and through vessels. The hanging aerial plants, water usually flows from high roots growing very vigorously alongside demand on energy resources. vascular cylinder. roots can be likened to branches of their soil water potential to low root water The occurrence and distribution of others, in the same conditions, that parent stem. Water moves from branch potential, and is then transported aerial roots in F. microcarpa trees, and were hardly growing at all. Initiation Characteristics and ability to In new aerial root tips of F. microcarpa, to aerial roots through vessels in the up the stem and leaf by evaporation. the initiation and elongation of aerial of new roots and elongation of existing absorb water cells in the cortex and vascular flexible aerial roots. The reverse may occur if the water roots was highly variable. Trees growing roots was clearly related to high levels of cylinder are closely arranged with few potential gradient is reversed.21 Some in identical conditions often had very atmospheric humidity (relative humidity The structural characteristics of aerial intercellular spaces. The endodermis The role of radially orientated ray tissue experiments show the water can flow different aerial rooting patterns. Even in and rainfall). Substantial growth was root tips and flexible aerial roots of F. is also not clearly defined. This would is the uptake of water through the outer into limbs under external pressure very wet conditions, some roots grew, recorded in the wet summer months, microcarpa observed in this study can be suggest that new aerial root tips cannot surface of twigs20. The well-developed through xylem vessel of cut limbs.22,23 others did not. while no growth was observed during compared with root tips, flexible aerial absorb water and conduct it to the xylem rays observed in transection of the The external pressure plays an important role in uptaking water through leaves When aerial roots did grow, it was at Growth rate Relative Rainfall and branches. Aerial roots of other plant times of the year, in environmental (averaged across samples from eight trees) Humidty types such as epiphytic orchids have conditions, and at locations within been shown to be anatomically adapted the canopy and on the originating Maximum daily Monthly total Monthly Monthly total to absorb water.24,25 Epiphytic orchids branch, that were associated with wet (mm) (mm) mean (mm) uptake water and nutrients efficiently atmospheric condition. This supports July 2014 10.1 187.8 80% 260.5 via a multilayered velamen arising from the common belief that their presence August 10.8 201.3 81% 548.2 the epidermis.26,27 But aerial roots of F. and growth is linked to water availability. September 8.0 73.7 77% 140.6 microcarpa do not have such anatomical October 4.1 12.1 71% 109.8 features. From the detailed study of the cellular November 0.3 1.1 78% 31.1 structure of the aerial root tips, however, December 0.0 0.0 67% 44.7 Liu (2011) observed that aerial roots of it was clear that the secondary vascular
January 0.0 0.0 72% 41.7 F. microcarpa have CO2 and water vapor tissues and cells are not closely arranged, February 0.4 1.2 78% 32.0 exchange functions, and concluded that and they do not have structures to March 5.1 38.3 85% 28.4 new aerial roots were active in CO2 intake absorb water. The more mature, flexible 2 April 11.9 196.2 77% 65.4 and H O release, and flexible aerial roots aerial roots were observed to have May 12.4 244.9 85% 513.0 had weak respiration and transpiration structures (lignified surface tissues, activity. Aerial root tips could only many vessels and medullary rays) June 2015 10.5 198.7 80% 291.0 absorb water in very high (almost 100%) that would allow the absorption and Table 2. Observed growth rates of aerial roots relative humidity. In flexible aerial roots, movement of some water, but as Liu28
82 / Yuan Lin 2015 Planting Futures Yuan Lin 2015 Planting Futures / 83 observed, this only occurred under high References 19. Esau, K. (1953). Plant Anatomy. Chapter 17. levels of atmospheric humidity As roots The root. John Wiley & Sons, INC. 470-529. 1. Liu, Liying, Fu Xiangzhao, Luo zhiqiang, Guo were observed to be growing throughout Xinxiang. (2011). Gas exchange characteristics 20. Katz, C., Oren, R., Schulze, E.-D., & Milburn, J. periods where relative humidity was of aerial root and affecting factors of Ficus (1989). Uptake of water and solutes through relatively low (70-80%), rapid elongation microcarpa (In Chinese). 19(1): 45-50. twigs of Picea abies (L.) Karst. Trees. 3(1): 33- of the root tips is most likely to be 37. 2. Pryor. M (2015) Street tree planting in Hong based on water (and nutrients) drawn Kong in the early colonial period (1842-98), 21. Cook, R., & Papendick, R. (1972). Influence up from terrestrial roots and conducted Journal of the Royal Asiatic Society Hong Kong of water potential of soils and plants on root along branches. The presence of many Branch 2014. disease. Annual review of phytopathology. conducting vessels and well developed 10(1): 349-374. 3. Ford, C. (1872). First annual report on the medullary rays in the cellular structure Government Gardens and Tree Planting 22. Baxter, P., & West, D. (1977). The flow of of flexible aerial roots suggest that their department, HKGG, 1 February 1873. water into fruit trees. II. Water intake through function is the transportation of water Surveyor General's letter to the Acting a cut limb. Annals of Applied Biology. 87(1): rather than its absorption from outside. Colonial Secretary on 'Tree Planting'. HKGG 103-112. 17 November 1877. Chinese Banyan (Ficus microcarpa L.f.), also referred to as F. retusa 23. Granier, A., Anfodillo T., and Breda, N. (1994). The link between the aerial root growth or F. nitida at the time. Axial and radial water flow in the trunks of of Chinese Banyans and wet conditions, oak trees: a quantitative and qualitative therefore, may be associated with their 4. Fortune, R. (1852). A Journey to the Tea analysis. Tree Physiology. 14(12): 1383-1396. Countries of China. John Murray, London ability to take advantage of wet ground 24. Zhang, Z. (1995). Anatomical structure of the conditions, i.e. uptake water through 5. Pope Hennessy, J. ‘The Governor’s Report’ nutritive organs of Dendrobium candidum. their terrestrial roots and move it quickly HKGG 29, April 1881. para 133. J Anhui Agri Univ, 1995, 22(3) : 301- 304. (in within trunk and branch structures, Chinese) 6. Jim, C. Y. (2014). Ecology and conservation rather than an added capacity of of strangler figs in urban wall habitats. Urban 25. Li, M., Su J. L., Wu R. H., et al (2001) absorbing water through the aerial roots Ecosystems, 17(2), 405-426. Anatomical study on the nutritive organs of themselves. Dendrobium candidum. J. Henan Agri Univ, 7. Pryor, M. Demystifying Tree Transplanting. 2001, 35(2) : 126- 129. (in Chinese) In proceedings of the International Arboricultural Society Hong Kong Conference 26. Bowes, B.G. and Mauseth, J.D. (2008). Plant 2010, Hong Kong (November 2010). structure. A colour guide, Second Edition. Manson publishing. 8. Wu, Z. Y., P. H. Raven & D. Y. Hong, eds. (2003). Flora of China. Vol. 5. Science Press, Beijing, 27. Zotz, G., Winkler, U. (2013). Aerial roots and Missouri Botanical Garden Press, St. of epiphytic orchids: the velamen radicum Louis. 37-71. and its role in water and nutrient uptake. Oecologia. 171(3): 733-741. 9. Hong Kong Herbarium , HK Plant Database
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16. Author’s unpublished research on sources of damage of trees during transplantation
Mathew Pryor is Head, and Li Wei is a 17. Liu (2011) Research Assistant, of the Division of 18. Kapil, R.N. and Rustagi, P.N. (1966). Anatomy Landscape Architecture, at The University of the aerial and terrestrial roots of Ficus of Hong Kong. benghalensis. Phytomorphology. 16: 382-386. Lignified aerial roots on Ficus elastica, on Lugard Road, The Peak
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