Meiosis and Pollen Mitosis in X-Rayed and Untreated Spikelets of Eleocharis Palustris

R E CE NT L Y, it was suggested by several authors that the family Cyperaceae has chromosomes with a »diffuse» centromere.Such chromosomes show centromere activity along their whole length, daughter chromosomes separating parallel to one another during anaphase.SCHRADER (1935) first pointed out the occurrence of this peculiar anaphase movement and used the term diffuse centromere.Some authors have spoken of »chromosornes lacking a localized centromere».Certain orders of insects (Hemiptera), Scorpions and Mites have such chromosomes (literature in LIMA- DE-FARIA, 1949).Insects having chromosomes with a diffuse centromere generally show so-called post-reduction in meiosis.The bivalents are not co-orientated at first metaphase and, thus, first anaphase is equational.Second anaphase is reductional.However, post-reduction may occur only in one sex or only in some of the bivalents (HELENIUS, 1952;SUOMALAINEN, 1953).Thus, chromosomes with a diffuse centromere may show pre-reduction.Among Thallophytes the class Conjugatae seems to possess chromosomes with a diffuse centromere (Spirogyra, GEITLER, 1930; Desmids, KING, 1953).Important was the discovery that the angiospermous genus Luzula has this kind of chromosomes.The Portuguese cytologists CAMARA, DE CASTRO, l"rALHEIROS, and GARDE (1947-1951) discovered and 'studied them in L. purpurea, a species with few (2n=6), relatively large chromosomes.This species was also studied by OSTERGREN (1949).The chromosomes are thick and show no constrictions.The Portuguese authors often stress the fluid nature of the matrix of the chromosomes, making them more sticky than ordinary chromosomes, At metaphase the chromosomes lie flat with their whole length in the equatorial plate, at anaphase daughter chromosomes move apart parallel to each other.During the anaphase movement the two ends of a daughter chromosome are bent towards the pole, whence it seems concave.