赤松

We recognize it everywhere in Japan that Pinus densiflora and P. Thunbergii generally grow in such unfavourable habitats as coast dune or waste mountainland. However, there is no fixed theory about its cause. We can conjecture that many special physiological characters will affect, but beside the ectotrophic mycorrhizas may have some causality on the pine growing. I observed, therefore, the external appearances and microtomic sections of ectotrophic mycorrhizas that were collected from various habitats, hoping to clear the difference among these mycorrhizas. The results are the following : (1) When the water content is enough and the humus is poor in the soil, the roots of the pine grow long and slender, then the roots branch off into many numbers and increase the root-hairs. (2) When the water content is moderate and the humus is rich in the soil, the pine has many roots and few mycorrhizas which consist of single mycorrhizas, not compound mycorrhizas. On the surface of many roots, fungus filaments spread a little and they don't form the fungus mantles. The more poorer humus in the soil, the more the single and compound mycorrhizas increase. In case of the humus and water content in the soil being very poor but aeration being sufficient, ectotrophic mycorrhizas deverope well and almost all of them become the compound mycorrhizas and a root can not be discovered. In this case the fungus mantles are very thick, being 15-45 μ in thickness. Hartig's network which is formed by two or three rows of fungus filaments deveropes well among cortical cells, in spite of the fact that it is formed generally by fungus filaments of one row. This resulted with the same tendency as the experiment of Moller's study on Pinus silvestris (3) In spite of the fact that ectotrophic mycorrhiza must deverope under such conditions as given under (2), becarese of water content and humus being very poor in the soil, when the soil is very compact and the aeration is unfavourable as in clay land, the ectotrophic mycorrhiza can not be formed and it become like the root of the seedling that was cultured in sterilized soil. It must braches off into many numbers and increase root-hairs in the ordinaly course as under (t), but it few branches off and has very few root-hairs. (4) When the ectotrophic mycorrhizas deverope well and the fungus mantles are very thick, the root is not found and the compound mycorrhizas increase. In the opposite case, roots increase and single mycorrhizas also are formed, but a compound mycorrhizas is not found. This may be due to the difference of stimulation which depending upon the quantity of Mycorrhiza-Producing fungi as Dr. Masui indicated.