In conclusion a brief summary of the facts and considerations here presented will be useful. 1. In Oenothera the heterotypic mitosis is a reduction division, separating whole chromosomes which lie successively on the spirem. The homotypic mitosis is an equation division, separating the longitudinal halves of the daughter chromosomes of the heterotypic mitosis. Whether an approximation of threads or a split in a single thread occurs in synapsis was not determined with certainty from the observations, but various considerations lead to the belief that in Oenothera the doubling is due to a split which closes up later, rather than to an approximation of separate spirems. 2. The conclusion that the method of reduction probably differs in different genera is based on two considerations: (1) the fact that in most of the recent accounts of synapsis and reduction in plants a side-by-side pairing of chromosomes from maternal and paternal spirems is described, while in Oenothera the members of a pair are arranged en...