A revised cytotaxonomy of the genus Tulbaghia (Alliaceae)

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104 VOSA Plate IV. (a) T. rhodesica Fries (x2). (b) T. violacea Harvey (x2). (c) T. violacea Harvey var. maritima Vosa (x4). (d) T. cominsiiVosa (x2). (e) The craggy hill of 'Unkomaninear Ofcolaco (Northern Drakensberg): from the top to the SW the habitat of T. transvaalensis Vosa. (f) Nabibia, small rocky inselberg about 75 km N of the Orange River with a population of Aloe dichotoma L. f: the typical habitat of T. tenuior Krause & Dinter.
CYTOTAXONOMY OF THE GENUS TULBAGHIA 105 The problem of the number of nucleolar organizers in Tulbaghia The number of nucleolar organizers in Tulbaghia vary from two to four and are of five types (fig. 22a). They differ in number and in combinations according to and characterizing the species (fig. 22b). Observation of silver-stained interphase nuclei in several species has shown that the amount of nucleolar material is very much equivalent whether there are two organizers or four. Thus, it seems that there has been an increase in the number of organizing sites with a proportional decrease in their nucleolar material and in its synthetizing activity. Silver-staining has also confirmed, in Tulbaghia, the intrinsic heteromorphism of the nucleolar organizers, and of their expression in the interphase nucleoli, which seems to be the rule in most organisms and based on a kind of dominance on the line of that demonstrated by NAVASHIN (1934) in hybrids between species of Crepis. The significance of the doubling of the nucleolar organizing sites must be found in the fine tuning of the interaction between the genome vis-a-vis the meiotic process and therefore on the inheritance and expression of certain adaptive features. The situation in T. violacea and T. cominsii, which share a very similar phenotype but with two organizers in the former and four in the latter, is rather interesting and demonstrates very well how little we known as yet on the very specialized biology and especially on the evolutionary meaning of such differences.
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A revised cytotaxonomy of the genus Tulbaghia (Alliaceae)

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