Although in past experiments connected with the physiology and ecology of the varieties of the rape plant a number of almost exhaustive investigations have been made of their vegetative organs, particulary of their external characters, the development of their generative organs has received compalatively little attention. While the experiments here referred to will be discussed in greater detail in a later paper, the authors, in this paper, merely attempt to establish criteria, with the aid of which it will be possible to measure the degree of growth of the generative organ in determining its development. Experiments covering this study were conducted during the period from 1939 to 1940 at the Konosu Farm of the Imperial Agricultural Experiment Station, using a variety of rape (Brassica napus L.) "Yokkaiti-Kurotane, " a variety which were preserved at the station. The seeds were sown on Sept. 27, 1939, under normal conditions. Special precautions were taken to have all the cultivating conditions as nearly uniform as possible, in order that the plants sampled from time to time for observation shall be as uniform as possible. Collections were made every third day from Nov. 2, 1939 to May 27, 1940. For the differentiation of inflorescence, a portion of the main stem, including the growing point, was fixed in CARNOY's fluid, and longitudinal or cross sections of from 13 to 17 μ thick were stained with either DELAFIELD's or HEIDENHAIN's iron haematoxylin. As soon as inflorescence became visible, the parts most developed, such as the bud, flower, and either siliqua or seed, that were obtained at the timae of sampling were used for material. The authors followed the extensive morphological changes that took place in the growing point and other parts during the growth of flower to seed, and established criteria by means of which the degrees of development of generative organs were standardized. Consequently, 38 principal stages of development, as shown in the microphotographs, were selected for the purpose. These stages are summarized as follows: 1. Stage of preparation for the first flower bud differentiation (Nov. 10-18) The dome-shaped vegetative corn assumes an elongated and swollen appearance (Pl. I, 1). 2. Stage of first flower bud differentiation, I (Nov. 21-24) Lateral protuberance arising near the growing point in the fundament from which the first flower bud intial originates. This primordium is distinguished from the leaf initials by its blunt and single ridge, its morphological significance marking the transition of growing point of the rape plant from the vegetative to the generative phase (Pl. I, 2). 3. Stage of first flower bud differentiation, II (Nov. 27-Dec. 2) The first flower bud that appeared in the preceding stage elongates upward (Pl. I, 3). 4. Stage of sepal differentiation, I (Dec. 6) Sepal primordia begin to differentiate from the tip of the flower bud, which last grows rapidly (Pl. I, 4). 5. Stage of stamen differentiation, I (Dec. 9) Stemen initials appear as papillae inside the sepals, so that the pistil primordium may be seen although signs of general differentiation are lacking (Pl. II, 5) 6. Stage of sepal and stamen differentiation II (Dec. 12-15) Primordia of sepal, of stamen and of pistil are more advanced than in the preceding stage. Sepals partly overlap the stamens (Pl. II, 6). 7. Stage of sepal and stamen differentiation III (Dec. 18-21). Sepals grow longer and overlap one another above the pistil, and the stamens increase in size. It is notable that the upper region of the pistil initial becomes flattened (Pl. II, 7). 8. Stage of carpel differentiation, I (Dec. 24). Carpel formation is first indicated by the appearance of a protuberance on the margin of the apex of the pistil, marking the end of the pistil concave (Pl. II, 8). 9. Stage of petal primordia differentiation (Dec. [the rest omitted]

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