THE theory of a reduction division in the spore mother cells of higher plants has gained considerable ground in the past two or three years; so that at present probably the majority of observers, who have devoted themselves almost constantly to the problems of the chromosomes, seem firmly convinced that one of the two mitoses in the formation of the tetrad is a "reducing" division. There is still, on the other hand, some diversity of opinion, and several years may elapse before cytologists will be strictly in accord upon this the most difficult of cell problems. One of the most important facts brought out by recent investigations is the shifting of the point in the tetrad formation, at which the qualitative separation of the chromosomes is held to occur, from the second, or homotypic mitosis, to the first or heterotypic division. Since it has been shown by FLEMMING and MEVES for the animal cell, and by GUIGNARD, STRASBURGER, and the writer, for the higher plants, that the daughter chromosomes of the heterotypic mitosis are split lengthwise as they separate in the metaphase, a more critical study has been devoted to the prophase of this division, and much light has been thrown upon certain obscure steps that have not as yet been satisfactorily explained. This double nature of the retreating chromosomes was regarded as a second longitudinal fission, since it could be seen that the spirem was double in a very early prophase.. This apparent second longitudinal division seemed to have proved beyond any shadow of a doubt that the second mitosis is not a reducing division, as has been so insistently maintained by many zoologists. Now that it has been shown that the homotypic mitosis in the spore mother cells of plants is not a reduction division, the question to be answered is whether in the heterotypic division the chromosomes are bivalent, or whether the segments of each pair separatealong the line of longitudinal fission.