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1. Different classifications of the taxs described here have been produced by formal taxonomists. The degree of relationship of the taxs, and their levels of importance have varied. Experimental taxonomists have produces a different picture, of a closely knit group with well defined relationships. 2. Genetics and cytology are used in this work in an effort to clarify the situation. 3. The control of characters of importance in classification is shown to be similar to that found in other groups. 4. A possible association between morphological characters and fertility factors is described, and compared with systems described in the literature. 5. The validity of cytological methods of determining relationships is discussed. 6. Melosis is a haploid plant is used to shoe the absence of autosyndesis, and hence to deduce that pairing in interspecific hybrids must indicate homelogies between specific genones. 7. The analysis of meiosis in interspecific hybrids is used to reveal relationships among the taxs. 8. The relationships of species revealed by dipoid melosis is confirmed by similar studies in polyploids. 9. Morphological data is used to provide a classification based on the methods of numerical taxosomy, and a comparison is made with classification of the group based on other methods. 10. A case is made out for considering all methods of revealing evolutionary relationships in the group equivocal. The relative positions of taxs to one another may reflect the rate evolutionary change, and whether speciation was allopatric or sympatric, rather then showing evolutionary relationships. 11. A classification is suggested which incorporates that best features of the experimental approach with one formal classification.