Cytological Studies in Artificially Raised Interspecific Hybrids of <i>Papaver</i>. III

Abstract

1. Pollen mother-cell in bud of an artificially raised interspecific F1 plant of Papaver somniferum and P. orientale (“F1 Papaver s×o I”) showed peculiar behaviour during their meiosis and the pollen-tetrad formation.2. After the first division of meiosis, several unusual types of cytokinesis, enumerated below, occurred in one and the saure anther, in addition to the usual interphase of P. M. C. where middle lamella initial (MLI) at the equator of the ist spindle is ephemeral: 1) the MLI persists through interphase and the 2nd division of meiosis, but no cleavage furrows appeared during the interphase; 2) MLI persists and the cleavage furrows appeared an both sides of the MLI, and their formation proceeded centripetally, beginning from the periphery of P. M. C. and followed by the protrusion of callose wall from the mother-cell wall; 3) the cleavage formation does not start all around the cell as in Gase 3) (ef. p. 408), but from one side ; in this rase the cell division was not generally complete; 4) two daughter nuclei are connected by a bridge formed as a result of the incomplete nuclear division; as a con-sequence, the P. M. C. is constricted, the notch of the constriction being fiiled with the callose membrane; 5) two daughter groups of divided chromosomes form a reconstruction nucleus, MLI and cleavage furrows do or do not appear.By the test with a corallin soda solution, the MLI reacts like the P.M.C. wall and indicates a callose nature; but the colour reaction is decidedly more intensive in MLI, when compared with that of the P. M. C. wall. MLI and P.M.C. wall do not fuse, although they come in contact with each other. The MLI-granules first appear as fine granules at the center of the equatorial plane of the spindle between the connecting fibers, and the depositing proceeds towards the peri-phery of the P. M. C.. When the ist MLI finally reaches the inner surface of the P. M. C. wall, it persists during the 2nd division; when the MLI does not reach the P. M. C. wall, it is probable that it dissolves before the interphase sets in, because the writer failed to find it in such an interphase, unlike the rase observed by JUEL in Hemerocallis. The thickness of the callose protrusion varied in different P. M. C., which certainly leave plasmodesmic connections between the daughter cells through the MLI and the callose lamella.3. In these P.M.C., the 2nd meiotic division occurs, so that suc-cessive as well as simultaneous pollen-tetrad formation, and also dyad and triad formations, were observed in one and the saure anther. From the above facts, it may be suggested that the saure gene or genes are responsible for the expression of these characters, at least in the present Gases, various modes of cytokinesis being modifications due to external influence.4. The persistente of the MLI and the cleavage formation, fol-lowed by the formation of callose protrusion after the ist meiotic division in P. M. C. of “F1 Papaver s×o” might have been caused by the delay of the 2nd division, i.e. Prolongation of the period of inter-phase probably due to an unusually low temperature. If such were really the Gase, an important factor in determining these characters would be the length of interval between the ist and 2nd divisions of meiosis.5. The MLI formation and its relation to the formation of the callose protrusion were traced in the ist and 2nd divisions of meiosis in P. M. C. of Allium odorum and in the 2nd meiotic division of P. M. C. of Crepis virens, and it was aseertained in these plants and in P. M. C. in “F1 Papaver s×o I” that the cleavage furrows always appeared along both sides of the MLI.