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C. gigantea collected from South India is found to be markedly distinct on both morphological and cytological characters. This species is outstanding in its cytology as it showed the presence of the aneuploid number of 12 distinctly large chromosomes which are rather unspecialized. This is an annual sexual species with normal meiosis and good seed setting. The size of the wings of the lower glume of the male spikelets of C. gigantea collectedfrom Calicut (Kerala) and Gopichettipalayam (Tamil Nadu) are narrower when compared with those of C. lacryma-jobi var. lacryma-jobi (local collection) which has very broad wings. Theleaves are long and narrow when compared with those of C. lacryma-jobi. The present study hasshown that the classification of the four species of Coix by Bor (1960) into two groups based on the size of the wings of the lower glume of the male spikelets appears to be invalid, eventhough C. gigantea agrees with this classification in the other morphological features and the ecological habitat.

C. taxon (2n=32) was found to be unique in its cytological and morphological features; its karyotype consisted of two distinct genomes. However, karyological studies of C. gigantea (2n=12) revealed a remarkable karyomorphology as the 12 distinctly large somatic chromosomes of this species resembled the 12 large chromosomes of C. taxon (2n=32) in dimensions and karyomorphology.The ability of C. taxon (2n=32) and C. gigantea (2n=12) to hybridize and produce F1 hybrids demonstrates a closer relationship between these two taxa. The hybrids were studied with respect to the morphological characters, karyotype and chromosome association at meiosis. Most of the PMCs of the F1 hybrids show regular pairing among the large chromosomes of both parents, resulting in the formation of six larger bivalents and therefore it is evident that the 12 large chromosomes of both taxa are genetically homologous. Phenotypically the F1 hybrids resembled more closely to the female parent, C. taxon (2n=32), in plant height, size and shape of leaves, size of involucre etc. It has been assumed from the unambiguous cytological evidence that C. gigantea (2n=12) has participated in the origin of C. taxon (2n=32). It is suggested that C. taxon (2n=32) is probably an amphidiploid, arisen by natural hybridization between C. gigantea (2n=12) and C. lacryma-jobi (2n=20) and subsequent doubling of the chromosomes.

Interspecific hybrids between Coix lacryma-jobi (2n=20 and its colchicine induced autotetraploid 4n=40) and C. gigantea (2n=20) were obtained and inter- and intragenomic chromosome homologies were studied. The diploid hybrid between C. lacryma jobi (2n=20) and C. gigantea displayed PMCs with chromosome numbers, 2n=19 and 20 even within the same anther. At meiosis, frequently 10 bivalents, and occasionally a chain each of 4 and 3 chromosomes and upto 2 univalents per cell were found. Two bridges with fragments were found at anaphase I. In the triploid hybrid between C. lacryma-jobi (4n) and C. gigantea (2n), a stable chromosome number of 3n=30 was found. Chromosomes mostly paired as trivalents. Higher associations of 4 chromosomes (not more than one per cell) were also found. The occurrence of bivalents in diploid hybrids and trivalents in triploid hybrids, despite the fact that the C. lacryma-jobi genome is in the duplicated state in the latter, indicates strong homologies between the genomes of the two species. However, the genomic divergence is reflected in the occurrence of univalents and formation of higher associations at prophase I and bridges and fragments at anaphase I, which indicate that the two genomes are separated at least by 2 translocations and 2 inversions. Judging from the basic number of 5 in the genus, the two species are considered tetraploids and it is believed that they arose from a common stock through polyploidy, differentiated subsequently through chromosomal repatterning. The occurrence of intragenomic bivalents in C. gigantea was deduced from chromosome associations in triploid hybrids. This shows that the haploid complement of 10 chromosomes of gigantea (as also lacryma-jobi) has two genomes, each of 5 chromosomes, which have partial homologies between them.

Detailed cytological studies have been made on Coix gigantea, which occurs as a pest in the paddy fields of South India. This species is mainly distinguishable by the size and shape of leaves which are rather long and narrow, resembling paddy leaves (and so this species may be considered to exhibit mimicry). The chromosome numbers of n=6 and 2n=12, have not been previously reported in this genus. This species is unique in cytological features also, as it shows distintly larger chromosomes. This is a highly stabilized species which shows perfectly regular meiosis with typical diploid behaviour.

Mixoploid plant showing a range of aneuploid PMCs from nullisomic (2n-2, 2n=18) to tetrasomic (2n+2, 2n=22) constitutions was isolated from a population of Coix gigantea. While majority of the PMCs were diploid carrying 2n=20 chromosomes, nearly 24% PMCs in some male racemes showed typical aneuploid chromosome configurations viz., 9II in nullisomics (2n=18), 9II+1I in monosomics (2n=19), 9II+1III or 10II+1I in trisomics (2n=21) and 11II or 9II+1IV in tetrasomics (2n=22). The chromosome configurational regularity among the aneuploid PMCs indicated that 2n-1 (2n=19) and 2n+1 (2n=21) constitutions probably arose through nondisjunction during one of the premeiotic mitoses in some sporogenous cells. Although difficult to explain the origin of PMCs with 2n-2 (2n=18) and 2n+2 (2n=22) constitutions, somatic pairing followed by nondisjunction during one of the premeiotic mitoses might lead to such situations.

Detailed cytological investigation has been made on Coix lacryma-Jobi var. ma-yuen, a soft-shelled cultivated taxon, collected from North East India. The count of 2n=30 for this species is the first hexaploid record for the genus. The previous reports have all been di-tetra or octoploids with a few aneuploids. Meiosis has been found to be somewhat irregular with a few multivalents and univalents along with bivalents in all the PMCs. The karyotype is unspecialized belonging to 1A category and the chromosomes are similar to the other varieties of C. lacryma-Jobi in size and morphology. The origin of this cyto-type is only speculative and the evidence indicates that it is probably a hybrid.

Higher polysomic constitutions occur very rarely among plants and animals and whenever they arise are constitutionally weak and usually highly sterile. A quadruple trisomic (2n=24, 2n+1+1+1+1) chromosomal constitution has been reported for the first time from among the selfed progeny of a spontaneous autotriploid (2n=30). Coix lacryma-jobi.Large number of PMCs showing four trivalents at diakinesis confirmed its quadruple trisomic nature. Inspite of polysomy this aneuploid is healthy and partly fertile.

The present investigation was undertaken with a view to explore the variational patterns of the mitotic chromosomes of maize and to examine the intergeneric re-lationships within the Maydeae. Twenty two cultivars of maize, mostly of Indian origin and one each of teosinte and Coix were analysed, employing the refined techniques of chromosome analysis.A wide variation was observed in the total chromatin lengths of the haploid complements. The cultivar CM-105 has the longest complement while Synthetic-B23 has the shortest complement. The karyotype is graded. The qualitative features of the ideograms are relatively uniform. The position of primary constriction varies from median to nearly submedian. Three types of chromosomes with secondary constriction were recognized, depending on the relative position of the two constrictions. Certain other variations were observed such as heteromorphic satellited chromosomes and haploid chromosome number in roots. The karyo-types of teosinte and Coix do not differ more than those of cultivars of maize.The gross chromosome uniformity of maize is well known and is the resultant of judicious human selection. The presence of gross chromosomal aberrations as the possible cause of the wide range of length variation in the chromosome comple-ments can be ruled out. Addition or deletion of nucleotypic DNA during the for-mation of the cultivars might possibly have played a role in causing the observed variation. Differential condensation patterns of the chromosomes, reflecting dif-ferent degrees of genetic activity have also been suggested to result in alterations of chromosome characteristics. In addition, several other factors such as minor aberrations, genetic differences, inherent length variability, nature of formation of the cultivars and differential response to the treatment may have acted individually and interacted with each other to produce the wide variation. Thus it has been shown that mitotic chromosome analysis, when carried at with appropriate tech-niques, brings out significant differences in maize.Evidences from several fields such as pachytene cytology, archaeology, paly-nology and comparative biochemistry indicate the close similarity of maize and teosinte. The present investigation does not warrant the segregation of maize and teosinte into distinct genera. The observations further support the inclusion of maize, teosinte and Coix in the Maydeae.

A change in the chromosome number of some PMCs in an interspecific hybrid of Coix L. (C. gigantea×aquatica, 2n=16) through cytomixis is reported. In the cytomictic PMCs the chromosomal changes are both quantitative, having 2n=13 and 2n=17 chromosomes instead of the usual 2n=16 and qualitative, having variable number of parental chromosomes instead of the usual 10+6 gigantea and aquatica combination. Causes, places, types, consequences and nature of cytomixis are discussed. It is argued that in the PMCs, the displacement of chromatin from its nearly central position towards periphery, as if acted upon by some force and in preparation to migration, cannot be without any purpose, the latter though as yest not clear to us.

A series of aneuploids, starting from nullisomy (2n-2 i. e. 2n=18) to hexasomy (2n+4 i. e, 2n=24), has been isolated from a natural wild population of Coix gigantea Koen ex Roxb., a member of the tribe Maydeae of Poaceae. Among a total of 96 aneuploids isolated, the various chromosomal variants appeared as: 68 nullisomics, 13 monosomics, 12 trisomics and one each a tetrasomic, a pentasomic and a hexasomic. Higher polysomics-the pentasomic and the hexasomic-are reported for the first time in plants.

In Job's tears (Coix lacryma-jobi L.) autotriploids (3n=30), hypo-triploids (3n=29) and hyper-triploids (3n=31) were produced by crossing diploids and colchicine induced autotetraploids. Trisomics (2n=21), double trisomics (2n=22) and multiple trisomics (2n=27) were obtained in the progenies of triploids. In none of the trisomics or double trisomics, the nucleolar chromosome was involved in trisomy. In each of the chromosome classes, meiotic behaviour, fertility and transmission of extra chromosomes to the progenies were studied. The average frequency of trivalents for a set of 3 chromosomes in triploids and aneuploids varied between 0.62 and 0.92, which is much higher compared to the average frequency of quadrivalents for a set of 4 chromosomes in the tetraploids (including hypo- and hyper-tetraploids) which varied between 0.49 and 0.58. These apparently indicate that the frequency of multivalents tends to decrease as the number of homologues of a chromosome in the complement increases. The average chiasma frequency per cell in triploid was significantly less than one-and-half times that in diploid. Although this depression in chiasmata in triploid is difficult to explain, some probable causes were mentioned. In general, aneuploids were lower in fertility compared to diploids, and both hypo- and hyper-triploids were less fertile than triploids. Transmission of extra chromosomes to the progenies occurred more frequently through the female gametes than male gametes.

Detailed cytological study in the tetrasomics of Coix gigantea Koen. ex Roxb. (Poaceae) has been carried out revealing a possibility of wider range in the gametic constitution than is generally predicted through breeding experiments. Although majority of the PMCs showed nine bivalents and a quadrivalent association at diakinesis, the four homologues gave two bivalents, bivalent and two univalents, trivalent and a univalent and rarely four univalents. Orientation and segregation in all these associations, especially irregularities involving quadrivalent and univalent, have resulted in gametes with from n=9 (n-1) to n=13 (n+3) chromosomes. There is every reason to believe that gametes up to n+2 (n=12) constitution are functional since polysomics, pentasomic (2n+3, 2n=23) and hexasomic (2n+4, 2n=24), have been isolated and cytologically studied by us in the past.

The morphology and cytology of an accession of Coix collected from Madhya Pradesh has been studied in detail. Morphologically the plants are distinct from all the species so far on record. The plants invariably possess 32 chromosomes, a number new to the tribe, Maydeae. Karyotypic analysis shows a pronounced assymetry with regard to the ratio between the longest and the shortest chromosomes and the proportion of acrocentric chromosomes. The distinctive morphology supported by the different karyotype warrants a specific rank for this form of Coix. The possible mode of origin of this new form has been discussed in detail.