219 the lateral epidermis; epidermis with the outer tangential walls strongly lignified, furnished with stomata opposite the chlorenchyma groups. Seta similar to the column but all cells with thinner walls, towards the apex the lateral bundles disappear and the chlorenchyma cells lie in close contact with the central bundle which is then surrounded by one or two layers of thin-walled cells. Caryopsis: starch grains compound, composed of numerous granules; embryo in sagittal section showing the presence of an extremely elongated epiblast, the lower part of the scutellum fused to the coleorrhiza, no cleft present at the base of the coleorrhiza and the scutellum bundle diverging below the coleoptile. The cross-section of the first embryonic leaf (sheathed by the coeloptile) with margins touching but not overlapping; the coleoptile with two lateral vascular bundles and the scutellum with one median vascular bundle (Fig. 4 E & F). C a p e .— George: Karoo in vicinity of Gauritz River, Ecklon s.n. Clanwilliam: Schlechter 8588; Welbedacht, Maguire 1855. Vanrhynsdorp: Ebenezer at Olifants River, Drege 8105; Zandkraal locally abundant in Marginal Strandveld, Acocks 14736; 2 m. N. of Vanrhynsdorp, Schweickerdt 2558; Wiedou River, Barker 9483. Calvinia: Groot Toring, Acocks 18591. Namaqualand: Doom River Bridge, Taylor 997; Wallekraal, between Kamieskroon and Hondeklipbaai, Schweickerdt 2565. I r a q ,—Isbel Hamrin near Injana, Guest s.n. (N.H. 15797); Isbel Daramish-kan, Guest s.n. (N .H . 16003). It occurs in the arid parts of the south western Cape in areas with winter rainfall (Fig. 3), and is widely distributed in North Africa and the Middle East. The interrupted distribution of S. capensis follows a pattern similar to that of many species in the Gramineae and various other families (see page 304). This annual species is adapted to desert conditions. Guenzel (1921, p. 6) investigated the anatomy of the leaf-blade of S. capensis (as S. tortilis Desf.) and his observations agree fairly closely with the description given above. The specimen investigated by Guenzel was collected at El-Kantara in North Africa. PA RT 2 THE TRIBE ARISTIDEAE 2 .1 . H is t o r y 2 .1 .1 . Taxonomic Studies For a detailed discussion of the history of the nomenclature of the genus the reader is referred to Henrard’s introduction to his Monograph (1929) as well as Schweickerdt’s introductory remarks in his treatment of the South African species (1941). In the past, Aristida has almost invariably been placed in the tribe Stipeae which, in turn, is treated either as a distinct tribe or as a subtribe or a group of the Agrosteae. Since 1875, when Duval-Jouve studied the anatomy of the leaf-blade of two Aristida species, it has been know'n that the anatomy of this genus differs from that of Stipa, the type genus of the Stipeae. These anatomical differences were, however, not regarded to be of sufficient value to exclude Aristida from the Stipeae. and, should there have been no other differences between Stipa and Aristida, one would have been inclined to agree. Avdulov (1931), Prat (1936) and others have, however, shown that the type of anatomy of the leaf-blade is usually closely correlated with karyological and organographical characteristics. Probably influenced by these observations, Roshevitz (1937) transferred the genus Aristida to the tribe Sporoboleae. Roshevitz’s concept of the Sporoboleae is a wide one and includes very heterogeneous elements. Anatomically Aristida and Sporobolus, however, agree fairly closely and a distant affinity between Aristida, Sporobolus and the genera of the Eragrosteae, which have a generally similar anatomy, seems probable. A discussion of the relationship of the Aristideae with other tribes of the Gramineae is given later in this paper. 220 In 1940 Hubbard & Vaughan created a new tribe, the Aristideae, to accommodate the single genus Aristida but gave no description. In most recent works on the classification of the Gramineae this tribe has been accepted. A valid description by Hubbard appeared in Bor’s Grasses of Burma, Ceylon, India and Pakistan (1960). The latest account of the Aristideae was prepared by Pilger (1956, p. 118) edited by Eva Potztal, and posthumously published in the Pflanzenfamilien. In this treatment Pilger enlarged the concept of the tribe by including the two Australian genera Amphipogon and Diplopogon. The reasons why the latter two genera are excluded from the Aristideae by the present author are given on p. 221. 2.1.2. Anatomical Studies Duval-Jouve (1875, p. 319 and PI. 17, fig. 10) was one of the first to investigate and describe the anatomy of a member of the Aristideae. His drawing of Arthratherum pungens (Stipagrostis pungens) gives an excellent representation of the structure of the leaf-blade, and agrees closely with that of Stipagrostis namaquensis studied by the present author. In both taxa the presence of a single chlorophyll-bearing bundle sheath can be seen clearly. The most valuable study of Aristida undertaken up to the present is probably that of Holm (1901, p. 101-133), who came to many conclusions similar to those arrived at independently by the author of this study. Holm studied 32 species of the section Chaetaria, two species of section Streptachne and three of section Arthratherum sensu stricto. All these species have naked awns and were found by Holm to be characterized by having two chlorophyll-bearing bundle sheaths, or as he described them “ a double parenchyma sheath ”, as well as having the chlorenchyma arranged in radial “ palisades ”. All Aristida species possessing plumose awns, some of which had been referred to the section Arthratherum by various authors until Bentham and Hooker and Hackel transferred them to the section Stipa­ grostis, were found by Holm to possess a single chlorophyll-bearing sheath while the inner sheath was usually composed of thick-walled cells devoid of chloroplasts. On basis of these observations Holm (p. 129) suggested that the species with plumose awns and a single chlorophyll-bearing sheath should be removed from Aristida proper, the latter having naked awns and a double chlorophyll-bearing sheath. Henrard obviously also considered this possibility but for various reasons decided otherwise. Species of this group investigated by Holm are A. plumosa, A. acutiflora, A. brachyathera, A. ciliata, A. pungens var. pennata and A. pennata. Holm’s observations were fully verified in the present investigation and were shown to be applicable to the South African species. In addition Holm studied many other genera either purported to be related to, or ecologically associated with, the genus Aristida. None of these genera, however, exhibited a double chlorophyll-bearing sheath, a characteristic up to the present met with only in Aristida sensu stricto. Holm was one of the first authors to point out the difference between the chlorenchyma organization of Stipa, where the cells show no regular radial pattern, and that of Aristida, Muehlenbergia and Lycurus, where the chlorenchyma cells are radially arranged in a single row of “ palisades ”. Theron (1936, p. 4) apparently misinterpreted the structure of the bundle sheaths, so clearly described by Holm, and stated that he had not found constant differences in this respect between the species with plumose awns and those with glabrous awns. Theron investigated the anatomy of the leaf-blades using material taken from herbarium specimens only and probably did not have access to living or preserved wet material. This may explain the incorrect detail in many of his drawings. Failure to recognize the difference in the buncle sheaths of the sections Stipagrostis and Schistachne on the one hand, and the remaining sections on the other, led him to divide the species into “ anatomical groups ”, which have very little bearing on taxonomic relationship based mainly on organography. 221 Jelenc (1950) made a general anatomical study of the North African species of Aristida but, as in the case of Theron (1936), was apparently not aware of the work of Holm (1901). Jelenc, however, correctly interpreted the differences in the bundle sheaths of the plumose-awned and glabrous-awned species, but could not, as he states himself, interpret the structure of the chlorenchyma on basis of the slides prepared from dry material, nor could he detect any bicellular hairs as observed by Prat (1936). The presence of bicellular hairs was likewise not observed by Theron. In the present paper these structures are clearly illustrated (Fig. 157E). Jelenc pointed out the differences in the structure of the silicified cells in the epidermis of the two groups: being (1) circular in the species with plumose awns and (2) dumb-bell-shaped in the species with glabrous awns. Although the shape of the silicified cells is not of specific diagnostic value throughout, it nevertheless is usually a good indication of the affinities of the species. Several other authors have studied Aristida species in more generalized papers on grass anatomy but none of these has expressed opinions on the taxonomy of Aristida or its sections. Practically all the information contained in these papers strongly supports the evidence gathered by Holm and Jelenc and that presented by the present author. Papers mentioning only one or two species are the following: Volkens, 1887, A. ciliata; Guenzel, 1921, p. 3, A. pungens; Sabnis, 1921, p. 225, A. funiculata and A. hirtigluma; and Zemke, 1938, p. 399, A. ciliata. Several South West African species were investigated by Guenzel (1913, pp. 16-22). He reported on the presence of bicellular hairs in addition to unicellular long hairs, furthermore on the differences in the bundle sheaths of the plumose and non-plumose species. For the non-plumose group A. adscensionis and A. barbicollis and for the plumose group A. uniplumis, A. ciliata, A. obtusa and A. namaquensis are mentioned. Lommasson (1947) offered a critical appraisal of the interpretation of the homology of the “ double parenchyma sheath ” in Aristida.