ON TERMINAL SCLEREIDS AND TRACHEOID IDIOBLASTS BY T. ANANDA RAO (Botanical Survey of India, 14, Madan Street, Calcutta-13) AND K. J. MODY (Gujarat College, Ahmedabad) Received August 19, 1960 (Communicated by Dr. K. Subramanyam, F.^.~.)

INTRODUCTION

As far back as 1885, Heinricher observed in several plants the occurrence of enlarged storage tracheids either in a free state or at the terminus of vein ends. Solereder (1908) enumerated 24 families of dicotyledons in which several taxa showed the presence of enlarged terminal tracheids. He emphasised the need for further work on this subject. Haberlandt (1914) reported the occurrence of such storage tr~cheids and regarded them as local reservoirs for storage of water. Comparable tracheoid idioblasts are reported in several seed plants (Pirwitz, 1931, Pass, 1940). Foster (1956) designated such cell forms 'Tracheoid idioblasts'; they resemble tracheids in their spiral thickenings or pitted walls and differ from them in shape, size and topography. Recent investigations (Foster, 1944; Rao, 1957 a) indicated the existence of diversified types of terminal ceils at the ends of veins in a large or small vein islet. The present study was undertaken to assess the importance of such cells in comparative morphology.

MATERIAL AND METHODS

The materials were derived partly from fresh plants and partly from herbarium specimens. The writer is indebted to the Curators of Bogor Botanical Garden, Indonesia and New York Botanical Garden for the supply of fresh and herbarium specimens. Thanks are also due to the Director, Scientific Co-operation Office, UNESCO, New Delhi, for procuring her- barium specimens from the U.S.A. The technique of clearing the leaves is already outlined (Rao, 1957 a). B4 257 258 T. ANANDA RAO AND K. J. ]VIODY OBSERVATIONS Olacacece.--The presence of sclereids is not common in this family. Edelhoff (1887) and Colozza (1904) recorded the presence of diffuse sclereids in several species of Heisteria, Cathedra and Anacolosa. Recently Foster (1947) reported terminal sclereid-like cells in the leaf of Ptychopetali~m. Similar cell forms have been observed in certain species of Olax and Heisteria. In Olax scandens Roxb., O. wightiana Wall., and O. zeylanica L., the cleared lamina shows the presence of sclereid-like cells at the vain endings (Fig. 1). The terminal cells have an irregular form. Most of them are oblong, triangular or spherical and occur in twos and threes distinctly at the vein ends. The slightly sclerosed cells have a broad lumen. The cell wall shows innumerable pits and is devoid of helical thickenings. in agreement with the observations of Edelhoff (1887) and Colozza (1904) the present study has revealed the existence of short fusioid diffuse sclereids in the mesophyll tissue of Heisteria brasiliensis Engl., H. cauliflora Sm., and H. flexuosa Engl. However, the vein-ends in these taxa show the presence of irregularly shaped slightly thickened cells. They exhibit the same features as in the species of Olax. In H. chippiana Standl., H. lo71gipes Standl., H. nitida Engl., and H. scandens Ducke the lamina is free from sclereids. However, all these species posses slightly thickened cells at the vein-ends. Such cell forms are irregular in shape, possess abundant pits and are devoid of helical thickenings. Capparidacece.--Of the 58 species of Capparis examined, sclereids were found only in C. amygdalina Griseb., C. angustifolia H. B. & K., C. cyano- phallophora L., C. indica (L.) F. & R., C. jamaicensis Jacq., C. odoratissima Jacq., C. orbiculata Wall., C. rotundifolia Rottl., C. verrucosa Jacq. The sclereids of C. amygdalina, C. angustfolia, C. cyanophallophora, C. indica and C. jamaicensis are short and prop-like and show more or less uniform distribution in the lamina. Most of the sclereids are diffuse, verd- caUy disposed and do not show a terminal relationship with the vein ends. Storage tracheids with helical thickenings occur at the vein-ends. In C. angustifolia the sclereids are short cell forms and occupy the epidermal and palisade regions of the mesophyll. They are mostly pyri- form to fusiform and have a short unbranched plug-like process disposed amidst the epidermal cells. The main bulged portion is situated in the palisade region and does not show any forking, but the lower end is some- times forked. The sclereids have a thick straited wall. There is a broad On Terminal Sclereids and Tracheoid Idioblasts 259 median lumen in the bulged portion and a narrow or occluded lumen in the rest of the cell. The leaf is xeromorphic. In C. odoratissima, the sclereids exhibit the same pattern of distribution as in C. angustifolia but they are short, fusiform or filiform having a plug-like process in the epidermal region and branched or unbranched ending at the other pole.

In C. orbiculata, C. rotundifolia and C. verrucosa variously branched polymorphic sclereids with terminal disposition are found (Rao, 1953). They are short, filiform, irregular, asymmetricaland possess short processes which give them the characteristic gnarled forms.

In C. koi Merr., C. moonii Wt., C. pumila Champ., C. spinosa L., var. canescens and C. viminea HK.f. & T., the vein ends possess tracheoid idioblasts and slightly sclerosed sclereid-like cells. They are oval or semi- circular or irregular in shape. The cells have a broad lumen without any spiral thickenings. In C. angulata R. & P., C. callophylla BL., C. cerasifolia DC., C. micracantha De., C. salicifolia Griseb., C. spinosa L., C. subacuta Miqu., C. tweediana Eichl., and C. zeylanica L., the vein-ends are free from 'Tracheoid idioblasts' and sclereids. However, sometimes small dilated ceils are present at the vein-ends.

Vochysiacece.--Solereder (1908) reported the presence of much elongated, spirally thickened storage tracheids in the mesophyll of Vochisia rufa Mart., and branched sclerenchymatous cells and fibres in the leaf tissues of Lightia licanoides and Trigoniastrum hypoleucum respectively. The storage tra- cheids of V. rufa which are in connection with the tracheae at the terminations of the veins, are tubular and often traverse the entire thickness of the leaf in a perpendicular direction. " The vascular bundles of the larger and smaller veins in Erisma violaceum, Vochisia rufa, Salvertia convallariaecodora and Trigonia lcevis are provided with a sclerenchymatous investment of variable strength, but this is absent in Callisthene fasiculata and Trigonia volnensiana.

Of the 12 species of Voehisia, sclereids were present in V. elliptica Mart., V. furcanosum Mart., V. ahupensis Spr., and V. magnifiea Warm. They are terminal or subterminal and not abundant. The sclereids have slightly sclerosed cell wall and lumen of irregular width. The sclereids of V. magnifica are more or less spherical or sub-spherical. The lamina exhibits prominent terminal traeheids. Terminal tracheids have prominent spiral thickenings whereas terminal sclereids possess slightly sclerosed walls and pits in abun- dance. This situation is similar to Memecylon leueocarpum (Rao, 1957 a). B5 260 T. ANANDA RAO AND K. J. MODY In 11. calophylla, the veins and vein-lets are densely covered with scleren- chyma. Mostly they extend beyond the vein-end as in Mimusops hexandra (Rao, 1951) and Uvaria macrophylla (Rao, 1953). In V. parviflora Spr., the sclerenchyma accompanying the veins extends beyond the vein-ends. In V. tomentosa Dc., and V. parviflora Spr., sclereids are absent but the vein-ends possess prominent tracheoid idioblast of varied shape and size. Sclereids and terminal tracheoid idioblasts are absent in the leaves of V. cinnamomea Pohl., V. ferruginea Mart., V. hcenkeana Mart., and V. laurifolia Warm. Goodeniacece.--The leaf anatomy of members of Goodeniace~e is in- completely known (Solereder, 1908). The occurrence of peculiar tracheoid idioblasts in a few species of Scaevola prompted me to examine the range of distribution and variation in some of the available species of Scaevola. Of the 18 species of Scaevola examined sclereids were encountered only in S. anchuscefolia Bth., S. canescens Bth., S. glabra H. & A., S. glandulifera Dc., S. globulifera Labill., S. holosericea De Vriese, S. hookeri F. Muell., S. lanceolata Benth., S. longifolia De Vriese, S. lobelia Murr., S. sp., and S. tripida Cav. Cleared leaves show that sclereids are of diffuse type and appear either as idioblasts or in groups of twos and threes in the mesophyll. They are polymorphic and range from simple globular, or rectangular to forking gnarled cell forms. Mainly there are three form types: Type L--Spherosclereids. They are seen in Scaevola sp. and S. holosericea. Sclereids are spherical or subspherical with much branching in Scaevola sp. whereas in S. holosericea the spherical or subspherical sclereids exhibit a strong trend towards bigger size and some of them become rectangular with number of processes at the corners. The transection of S. holosericea reveals the uniform distribution of these curious sclereids especially on the adaxial side and they form prominent cells inside the lamina. Irrespective of their varied forms the cell wall is sclerosed and exhibits striations often dotted with pit canals. The lumen is irregular and devoid of crystals. Type H.--Polymorphic, small rectangular cell forms. They are en- countered in S. anchuscefolia, S. canescens, S. glabra, S. glandulifera, S. globulifera, S. hookeri, S. lanceolata, S. longifolia and S. tripida. The sclereids are small rectangular cell forms with striated thick sclerosed wall and possess irregular lumen. Inside the lamina they are present as isolated cells and very rarely in groups of threes and fives, but in no instance they were found to fuse together. It is not uncommon to observe 'sclerocysts' in S. glabra. The sclerocysts are composed of 3-5 cells closely juxtaposed and unlike On Terminal Sclereids and Tracheoid Idioblasts 261 the sclerocysts of Memecylon parviflorum (Rao, 1957 a) they do not encircle the vascular bundles. Type IIL--Sclereid-like cell at the vein-ends. Such cell forms are seen only in S. saligna and S. lobelia. They are spherical or sub-spherical forms present at the vein-ends along with prominent traeheoid idioblasts (Figs. 2-5). The cell wall is slightly selerosed and straited. Most of them are spirally thickened or sometimes they possess a wide lumen of irregular pitting. Similar cell forms are seen in Capparis religiosa and Olax sp. In S. dajoensis Merr., S. oppositifolia Roxb. and S. chamissoniana Gaud., the vein-ends are free from sclereids and storage tracheids whereas in S. crassifolia storage tracheids of varied shape are present at the vein-ends. It is not uncommon to observe slightly sclerosed diffuse forms in the lamina of S. hookeri and S. fruteseens.

DISCUSSION The present study shows the existence of different forms of terminal cells. In the majority of the investigated species, the terminal cells are either sclereids or tracheoid idioblasts. However, the existence of inter- mediary cells is reported in certain species of Mouriria (Foster, 1946), and Memecylon (Rao, 1957 a) and this investigation shows their presence in certain species of Olax and Capparis, Seaevola and Vochisia. It is now worthwhile to compare sclereids and tracheoid idioblasts. Between them there are certain common features. Sclereids are terminal, diffuse or of the mixed type. Similarly tracheoid idioblasts are situated at the vein- endings or as diffuse idioblasts (Solereder, 1908; Habarlandt, 1914; Pirwitz, 1931; Pass, 1940; Foster, 1956; Rao, 1953, 1957a, 1957b). Foster (1947) reported terminal selereid-like cells in the leaf of Ptychopetalum (Olacacea~). In pattern of distribution there is a good deal of similarity. In certain species of Olax (Rao, 1957) the terminal sclereid-like cell resemble certain tracheoid idioblasts which occur in Capparis religiosa (Pirwitz, 1931). Both exhibit a varied shape and size in the same leaf. Sclereids and tracheoid idioblasts also resemble in their ontogeny. Just as tracheoid idioblasts originate from adjacent cells of the ground meristem (Pirwitz, 1931) sclereid ontogeny has revealed a similar type of origin. However, the mature sclereids differ from the tracheoid idioblasts in one respect. Sclereids have slightly or heavily sclerosed cell wall with pits, whereas, as a rule, the tracheoid idioblasts are thirl-walled with pitted secondary walls. Another distinguishing character is that while certain tracheoid idioblasts show the presence of spiral thickenings they are not present in sclereids. 262 T. ANANDA RAO AND K. J. MODY

The present study supports the view (Rao, 1953, 1957 a, 1957 b, 1958) that the genus which has well-developed terminal tracheoid idioblasts will have some species or all sp~'zies with well-developed terminal sclereids. it is further seen that in a genus exhibiting tracheoid idioblasts and terminal sclereids sometimes it is not uncommon to observe in certain vein-ends the existence of intermediary cell forms. A clear example is seen in Mouriria (Foster, 1946), Memecylon (Rao, 1957 a), Niebhuria (Rao, 1958), and Cap- paris, Scaevola and Vochisia (Present study).

SUMMARY Contrasted forms of terminal cells have been observed in certain taxa of Olax, Capparis, Scaevola and Vochisia. The exact morphology of inter- mediary cell forms could only be known by studying their ontogeny in detail. The resulting data would throw interesting information on the question of homology among various types of cells.

REFERENCES

* Colozza .. Bot. ltal., 1904, 11, 539-65. Edelhoff, E. .. Engler. Bot. Jahrb., 1887, 8, 100-53. Foster, A. S. .. Bull. Torrey hot. Club, 1944, 71, 302-.26. .. J. Arnold Arbor., 1946, 27, 253-71. .. American .1. Bot., 1947, 34, 501-14. .. Protoplasma, 1956, 46, 184-93. Haberalandt, G. •. Physiological Plant Anatomy, 1914, MacMillan & Co, London. Heinricher, E. .. Bot. Zbl., 1885, 23, 25-53, 56-61. Pass, A. .. Bot. Zeitschr., 1940, 89, 119-64, 169-210. Pirwitz, K. .. Planta, 1931, 14, 19-76. Rao, T. Ananda .. J. Indian Bot. Soc., 1951, 30, 28-29. .. "Studies on foliar sc!ereids in seed plants," Ph.D. Thesis, 1953, Mysore University, India. .. Ph.vtomotphology, 1957a, 7, 306-30. .. Proc. Natl. lnst. Sci. India, 1957b, 23, 152-54. .. P~oc. Indian Acad. Sci., 1958, 48B, 223-28. Solereder, H. •. Systematic Anatomy of the Dicotyledons, 1908, I and 2, Oxford.

'* Not seen in original. T. Ananda Rao and Proc. Incl. Acad. Sci., B, Vol. Llll, Pl. XH K. J. Mody

FJGs. I-5. Cleared leaf portions showing diversified types of terminal cells. FIG. 1. Olax scandens, X 200. Figs. 2-5. Sctevola lobetia. × 200 each.