The flax wilt disease caused by Fusarium lini, gives the most destructive injury to the crop and it has been proved that a certain crop-rotation for long interval, to be only the effective method for the prevention of its occurrence. But the breeding of some resistant strains to the disease should be the most desirable thing in the flax cropping. Since 1902, under the direction of Professor MINAMI, the successive cropping experiment of flax has been made at the experimental field of the Hokkaido Imperial University, and in the course of that experiment an excellent flax strain being resistant to the wilt disease was bred true from Riga variety. The present paper reports the nature of the resistant strain (marked MR in thjs work) comparing with the original Riga variety (marked 0R) from a physiological standpoint. The experiments were carried out in two series to prove the influences of the soil moisture in one series and the influences of the soil temperature in the other upon the occurrence of the wilt disease. The materials were grown principally on thc sick soil which was taken from the field, where the successive cropping experiment has been carried on. Firstly, in order to control the soil moisture of each pot, the writer used the LIVINGSTON's auto-irrigator, regulating its mercury column in height of O, 1, 3, 4 or 7.5 cm., in which the percentage of soil moisture was actually found to be 55.1, 55.0, 47.0, 43.0 or 35.8 respectively. Secondly, an experiment was carried out to ascertain the influence of soil temperature ranging from 15° to 40°C, Each plot was controlled approximately at intervals of 5°C, The results of these experiments are summarized as follows: 1. In relation to the difference of the soil moisture content, OR and MR showed generally a marked difference in susceptibility to the wilt disease; OR wilted more severely in low soil moisture (35.8%) showing about 68% of wilted plants, while in higher moisture content (55%) the percentage of the occurrence of the wilt was about 42%. On the contrary, in the same condition, MR showed the percentages of wilted plants ranging from 0 to 2.1%. As this set of experiment was carried out in the green-house, the soil temperature fluctuated between 15°--22°C, which is not a very favorable condition for the occurrence of the wilt disease. 2. Results of the experiment in regard to the control of soil temperature are summarized in the following table: Percentages of wilted individuals on the 20th days after germination at various soil temperatures (The moisture content of soil was uniformly kept at ca. 44%) [table] 3. From the above result, it will be understood that: (a) At the temperature below 30°C, OR shows higher susceptibility than MR. (b) In the case of OR, the optimum temperature for the occurrence of the wilt disease ranges from 25°C to 30°C, while in MR it is 30°C or a little higher. (c) Above 30°C OR shows higher resistance than MR. 4. To learn the protoplasmic difference between two strains, epidermal or subepidermal cells of hypocotyle were compared by means of plasmolysis. As plasmolytica 0.3-0.5 mol. sugar solutions were used. It was very interesting to note that MR showed a higher percentage of " Krampfplasmolyse " than OR. 5. The protoplasmic character (Krampfplasmolyse) of MR was compared with those of other 12 varieties of flax, and MR showed excessively high percentage of " Krampfplasmolyse " among all of them. 6. It was noticed that the appearance of these two kinds of plasmolysis varied in accordance with the change of the soil temperature, and it seems also to have some relation with the change of the percentage of the wilt disease. 7. From the above results it is considered that the physiological character of the protoplasm may have a certain relation with resistance of this MR strain.

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1. The resting nucleus of the pollen mother cell of Linum usitatissimum contains prochromosomes distributed irregularly throughout the nuclear cavity, but always connected with the reticulum (Fig. 1). 2. With the beginning of the nuclear division occurs the contraction of the nuclear contents away from the nuclear membrane, and at the same time takes place the conjugation of the prochromosomes in pairs (Fig. 2). 3. In the synapsis stage it is observed that the spireme is connected with the nucleolus at one point, its pole ( Fig. 3). Perhaps the contraction of the nuclear contents which occurs in the synapsis stage is due to a concentration of the spireme toward the pole of the nucleolus. During the synapsis stage, the nucleolus produces generally one, rarely two or more, secondary nucleoli (Fig. 3). These sccondary nucleoli connect with the nucleolus at its pole. 4. At the late pachytene stage the spireme seems gradually to lose its chromatin, until all the spireme becomes nearly colourless and enters the achromatene stage (Fig. 5). 5. After the achromatene stage, pairing chromatin appears on the spireme which is connected with the nucleolus (Fig. 6). Perhaps during this stage a movement of chromatin may occur from the nucleolus to the connecting spireme. 6. At the beginning of the first telophase occurs a movement of chromatin from the chromosomes along the fine threads, which connect them with each other, to form irregular masses of chromatin (Fig. 10), and finally all the chromatin concentrates in one place to produce a new nucleolus (Fjg. 11). During this stage, some of the chromosomes disappear, completely losing their chromatin, while others remain as small granules in the nucleolus retaining part of their chromatin (Fig. 11). 7. During the second prophase, the small granules of chromatin seem to reform the chromosomes, gradually receiving chromatin from the nucleolus (Figs. 12 an 13). In the second telophase the same phenomenon as in the first telophase occurs that the chromatin of the chromosomes concentrates in one place to form the new nucleolus (Figs. 14 and 15). These facts indicate that the nucleolus contains the material of the chromosomes. 8. The haploid number of the chromosomes in Linum usitatissimum is fifteen.

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As shown in Table 1, in the research conducted in 1931 as to the development of fruit in the bunch type of peanut, the upper seed in the pod became much larger in size and weight than the lower, but in the similar experiment conducted in 1932 such phenomenon was not found, because the upper seed never exceeded the lower. In the present experiment the author has tried to discover the causes responsible for these changes in the size and weight of the seeds according to the position in the pod. The experiment was carried out in the open field in 1933 with the same variety, " Java small-seeded No. 3 ", as used in the experiments above described. Removing the ovaries from the soil 15 days after their initial soil-penetration, they were divided into two groups according to whether the upper position of the pod was made to face (1) downwards or (2) upwards. The pods were in both cases subsequently buried anew in the soil for 35 days, i.e. 50 days after their initial soil-penetration, after which they were once more taken out and the form and weight etc. of the pods and the seeds belonging to each group were compared with one another. Each group consisted of 15 pods and the average figures per fruit were shown in Table 2. According to the table, the upper seed is larger but not so wide as the lower seed whether in the case of the facing the pod upwards or downwards. This phenomenon will be stated in the future report upon the development of the fruit. As far as volume, fresh weight and dry weight are concerned, the upper seed is inferior to the lower in the case where the pod faces upwards, but the upper is superior to the lower in the case where the pod faces downwards; i.e. the lower seed grows larger in the former case, and the upper seed develops more in the latter. As mentioned above, the position of the pods under the ground has an effect upon the ratio of growth between the upper and the lower. It is clear therefore that the seeds located on the lower side are generally larger than those on the upper side, no matter whether they may happen to be upper or lower seed in the pod itself. This phenomenon seems to be connected with the translocation of the nutrient elements in the tissue. Though the difference above mentioned between the results of two experiments carried out in 1931 and 1932 may be produced by various factors, the fact deduced from the present experiment may be counted as constituting one of the important factors. It may be possible to infer from those results that physiological causes such as the soil conditions and oxygen content in the soil, and mechanical causes such as subterranean abstruction may bring about changes not only in the development of the ovary and seed themselves, but also the position of seed in the pods executes certain influences on their development.

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