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Plate 1.-Coriandrum sativum var W.B, •. Plate 2.-Coriandrttm sativum var W.B" Somatic metaphase with 2n = 22 chromosomes. Plate 3.-Coriandrum sativum 246. Plate 4.-Coriandrum sativum 157. Diakinesis showing n = 11 bivalents. Plate 5.-Coriandrum sativum 153. Metaphase II showing n = 11 chromosomes. Meiotic irregularities of Coriandrum sativum. Plate 6.-Anaphase I showing late separation. Plate 7.-Anaphase II Showing late separation and tripolar formation. Plate 8.-Showing triad formation. STUDY OF THE STRUCTURE AND BEHAVIOUR OF CHROMOSOMES 447 Name of the varieties Coriandrt!m sativum var.

The genus Apium belongs to the subtribe Carinae, of the tribe Ammineae of the family Umbelliferae. It is an important genus of which several varieties have commercial importance and it is widely cultivated.Most of the species of Apium are diploid with 2n=22 chromosomes

Cytotypes within the genera Seseli L. and Oenanthe L. show variation in chromosome number in pollen mother cells. A correlation of low chiasma frequency with meiotic irregularities and pollen sterility was noted. In addition to the meiotic irregularities in the two genera occurrence of polyspory and triple pollen formation during meiosis have been observed in Seseli diffusum (Roxb.) Sant. Wagh. The presence of different chromosome numbers in different populations of the same species and karyological investigation in 4 species of Oenanthe L. suggests that structural changes of chromosomes associated with numerical differences have possibly played a role in their evolution. Diminution in chromosome size and complete absence of metacentric chromosomes in Oenanthe lachenalii Gmel. suggest that probably this species is more evolved than 3 species of Oenanthe (i.e., O. benghalensis Benth., O. pimpinelloides L. and O. thomsoni Clarke). The interrelationships of the two genera are discussed.