Morphometric and karyological study of Genista sericea (Cytiseae-Fabaceae)

A morphometric and karyological study of several populations of Genista sericea, a northern Illyrian amphiadriatic species, with a disjunct distributional area centered on Pollino Massif (southern Italy), has been undertaken, based on herbarium specimens and field research. Morphometric analysis allowed to individuate three distinct groups of populations which are here attributed to three taxa at subspecific level. One of them is here newly described: G. sericea subsp. pollinensis, endemic to northern Calabria in Pollino and neighbouring areas of Basilicata. The taxonomic status of G. sericea var. rigida was re-evaluated and a name of a new rank is proposed: G. sericea subsp. rigida (occurring in southern Illyria), while subsp. sericea is a southeastern Alpine northern Illyrian taxon. The names G. sericea and G. sericea var. rigida are lectotypified. Karyologically, all the taxa are characterized by the same somatic number 2n = 48, sometimes with B chromosomes (up to four).

CYTOTAXONOMIC OBSERVATIONS IN THE GENUS AESCHYNANTHUS(GESNERIACEAE)

This study is a contribution to the further understanding of cytological patterns in Aeschynanthus(Gesneriacaeae). Chromosome numbers are reported for 12 species from six sections; nine of these are new counts. Two basic numbers, x=16 and x=15, are generally encountered. Aeschynanthus gracilis proved to be of exceptional interest, as its rare somatic number, 2n=28, confirms the occurrence of a third basic number, x=14, in the genus. Variation in chromosome number in relation to seed morphology is examined.

CHROMOSOME NUMBERS OF SOME TROPICAL RHODODENDRONS (SECTION VIREYA)

Chromosome counts for 27 species plus one intersubsectional hybrid are presented from all seven subsections of section Vireya in the genus Rhododendron. Twenty-three are new, and five confirm previously published counts. The plants originate from a wide geographical and altitudinal range; all have a uniform somatic number of 2n=26.

Variation in chromosome number in the Manuleae (Scrophulariaceae) and its cytotaxonomic implications

Chromosome numbers for 11 genera and 36 species in the predominantly South African tribe Manuleae (Scrophulariaceae) are presented, the majority being first reports. The basic numbers of the genera form a dysploid series, x = 6, 7, 8, 9. The somatic number of most of the species is diploid, ranging from 2n = 12 to 2n = 18; that of Jamesbrittenia, 2n = 24, is probably of polyploid derivation. The highest somatic number encountered in this survey is that in Camptoloma lyperiiflorum, with 2n = c.56, which, taken in conjunction with a published count of 2n = 28 for another species of Camptoloma, is octoploid based on x = 7. This is the only example, so far, of intrageneric polyploidy in the Manuleae. The somatic number in certain genera appears to be constant over some subgeneric divisions (e.g. Jamesbrittenia, 2n = 24), but variable in others (e.g. Sutera, 2n = 12, 14). The variation in chromosome number observed in this study parallels and corroborates the redefinition of generic boundaries proposed by O. M. Hilliard. One species of Selago (in the tribe Selagineae) was also included in this survey for cytological comparison with Tetraselago (Manuleae).

CYTOGENETIC, ECOLOGIC AND MORPHOLOGIC STUDIES IN BRAZILIAN FORMS OF PASPALUM NOTATUM

The somatic number, meiotic behavior, morphology and ecology of five forms of Paspalum notatum are reported. All of them showed a chromosome number of 2n = 40. There is a fair degree of variation in the frequencies of meiotic chromosome configurations in different strains of a given form, but for four of the five we could characterize them as showing about 2-3 IV and 14-16 II. The type Capivari presents distinct differences in relation to all others, with about 1 IV and 18 II. The prevalence of I and III is very low (about 0.1) in all forms investigated. The morphological and ecological data, in a general way, confirm the difference between Capivari and the other taxons.

CYTOLOGICAL STUDIES IN SAMBUCUS

Karyotypes were determined for six taxa in the genus Sambucus, family Caprifoliaceae. Chromosome number determinations of 2n = 36 agreed with previous findings for S. canadensis and S. nigra of section Eusambucus and for S. ebulus of section Ebulus. Three taxa from the section Botryosambucus were found to have diploid numbers of 38: S. sieboidiana, S. racemosa var. arborescens and S. racemosa var. pubens. A Quebec population of the latter variety had a somatic number of 42. It is suggested that chromosome races in var. pubens came about through aneuploid gamete production in 2n = 36 ancestors and that their persistence may be related to their newly acquired ability to adapt to varying environmental conditions in the formerly glaciated areas.Differences in karotype within sections were small while between sections they were a little greater and rested mainly on variation in chromosome number, presence of satellites and number of telocentrics.

CYTOGENETIC, ECOLOGIC AND MORPHOLOGIC STUDIES IN BRAZILIAN FORMS OF PASPALUM DILATATUM

The somatic number, meiotic behavior, morphology and ecology of five forms of Paspalum dilatatum Poir are reported. The sexual type yellow anther (2n = 40) showed essentially regular meiotic behavior. The common form (2n = 50) presented 20 II and 10 I in about 85% of the cells studied at diakinesis and metaphase I. Pauciciliatum (2n = 40) and Uruguaiana (2n = 60) showed a wide range of chromosome configurations at these stages; finally, Torres presented uniformly 60 univalents. These results are compared with morphologic and ecologic data and some suggestions about the possible mode of origin of these forms are presented.

The Behaviour of the Nucleus during Spermatogenesis in Fasciola hepatica

1. The behaviour of the nuclei of the male germ cells of F. hepatica L., as observed after fixation in Carnoy 6:3:1, is described and illustrated. All phases of the division and maturation of the male germ cells occur within the multi-branched and tubular testes. The daughter cells by remaining in association and dividing synchronously throughout these divisions eventually give rise to a spermatid rosette of thirty-two component cells. During spermiogenesis the nucleus of each individual spermatid cell undergoes a progressive elongation and is converted into an undifferentiated and homogeneous filiform thread. 2. The occurrence of globules of unknown origin, composition, and function is recorded within the peripheral border of spermatogonial primordia. Pycnotic primordial spermatogonia are also observed to originate in the peripheral testis cells. 3. The cyto-morphology of the chromosome complement is recorded in relation to size and the position of the attachment-constriction. The somatic number in the male cells is found to be 12 (diploid). 4. From a study of metaphase configurations chiasmata are shown to exhibit a normal distribution and there is no apparent localization of the chiasmata. The infrequent occurrence of chromatid bridges at anaphase I is correlated with the retention of an unusually large number of interstitial chiasmata.

Meiosis in Oenothera missouriensis

A cytological study of the meiotic phenomena in Oenothera may not need an excuse in spite of the exhaustive studies of the genus made by numerous competent cytologists of this century. Up to the present time, all the investigators of Oenothera cytology have been successful in establishing that the basic ( n ) number of chromosomes in this genus is 7; although tetraploid (Gates, 1911), triploid (Cathcheside, 1931), and trisomic numbers might occur either naturally (by mutation) or could be produced by experiment. It is also known that the somatic number of chromosomes corresponds with the number of chromosome bodies in the diakinesis and metaphase of the heterotypic division.. Thus in diploid Oenothera species, hybrid, or mutant at the diakinesis of pollen mother cells 14 chromosomes have been shown to exist, withouth any doubt, in the configuration of a closed circle, in 7 ring pairs, or a mixtrue of free pairs and closed circles. Mathematically, there are 15 possible configurations in which 14 chromosomes can arrange themselves in the form of closed circle, ring pairs, or a combination of ring pairs and closed circles (Cleland and Blakeslee, 1931; Darlington, 1931). Of these 15 Possible configurations 13 have already been reported in various Oenothera species, hybrids and mutants (Darlington, 1931). Regarding the origin and significance of these chromosome configurations invsestigators have not yet reached an agreed opinion. Apart from the genetical significance, the much disputed cytological question of parasynaptic and telosynaptic methods of chromosome pairing is yet far from a final solution. In oenothera both the methods of pairing have strong sup-porters in consideration of observed cytological facts. The fact are (i) the continuous spireme (in leptotene stage); (ii) the pachynema and the diakinesis consisting of the 14 chromosomes arranged end to end. This arragement, known as catenation of chromosomes, favours the telosynaptic rather than the parasynaptic union. Wheras (i) double threads at the prophase, (ii) the looping of the threads, and (iii) the half number of bodies (7 ring pairs) at the diakinesis support the parasynaptic method of pairing of chromosomes. The occurence of a complete catenation of 14 chromosomes in some Oenotheras and the presence of 7 free pairs in others naturally suggests the question-whether they can be correlated with the two methods of chromosome-pairing in the meiosis of Oenothera .

The Cytological Aspects of the Determination of Sex in the Diœcious Forms of Lychnis

The present research is part of a more general inquiry into the conditions of sex determination in the genera Lychnis and Silene. This paper consists of an account of the cytology of the diœcious forms of Lychnis with special reference to sex chromosomes. Lychnis Flos-cuculi is referred to at times for the sake of comparison. The somatic number of chromosomes in L. dioica (agg.), as well as in L. Flos-cuculi L. Flos-Jovis, and Silene pendula, is twenty-four. The hybrid L. alba x L. dioica behaves in a perfectly regular manner and is practically indistinguishable cytologically from its parents. In Lychnis dioica (agg.) the pollen mother cells show a particularly close synizetic knot from which the spireme never opens out fully. Just before the second contraction the spireme becomes differentiated into thicker and thinner portions of which the thicker clearly represent the chromosomes. The thread becomes much shorter and stouter and, as the contraction figure, opens out, the chromosomes separate off in pairs forming typical bivalents lying either crossed or parallel. The reduction is thus typically telosynaptic and there is no trace of a split thread at any stage. As the bivalents contract, one pair is seen to be larger than the rest and to consist of two unequal portions, both of which are larger than the other chromosomes. At diakinesis, the bivalents become completely dissociated, once more giving twenty-four separate chromosomes. L. Flos-cuculi differs in haying ring-shaped chromosomes, both at diakinesis and on the equator of the heterotype spindle. In L. dioica (agg.), the large pair of chromosomes lies at the periphery of the metaphase plate and is seen to consist of one very large hooked member and one smaller, more pear-shaped, chromosome. Anaphase figures show the larger chromosome in the form of a cross, as seen from above, suggesting a double structure. There is no difficulty in distinguishing which member of the unequal pair is present in any given daughter plate. In the interkinesis there are two points worthy of note, (1) Several nucleoli are present, in place of the usual single one typical of all other stages. (2) The twelve chromosomes separate completely into halves, thus giving twenty-four bodies lying within the membrane, just as in diakinesis. At the ensuing metaphase the X and Y chromosomes are again most distinct, especially when the two spindles lie parallel. Megaspore development is briefly described. Meiosis is similar to that found in the male plant, except in relation to the large chromosomes. The large chromosomes are equal in size, and by careful comparison of size and shape, are shown to correspond to the small one of the unequal pair in the male. The Y chromosome is thus larger than the X, quite contrary to expectations based on the condition in animals. It is also probably double in nature though it does not separate into two parts, as far as has been observed. A brief review of the literature shows that in Rutnex there is a pair of Y chromosomes ; in Humulus and Vallisneria a double structure is presumed to be the X element, but on the basis of Lychnis may possibly turn out to be the Y instead. The cytological results above are shown to corroborate the results of the experimental work of Shull and Correns on the same forms.