1. The relation-ship between the light factors and the polyploidy in 8 Rubus species has been researched by the writer in their growing places in Ehime prefecture. The species of Rubus which were used in this research are as follows: R. parvifolius, R. Wrightii, R. palmatoides, R. hirsutus, R. phaenicolasius, R. Sieboldii, R. pectinellus and R. Buergeri. 2. The average value of the relative intensity of light at their growing places is as follows: 2X=72/100, 4X=54/100 6X=32/100 and 8X=34/100. Namely, the relative intensity of light of polyploid plants is larger than that of the diploid plants and the relative intensity of light decreases according to the duplication of the chromosome numbers. 3. The polyploid plants of Rubus seem to have got anew the special quality to grow well in the shade. The diploid plants are the deciduous, while the polyploid plants pass the winter ever green. The polyploid plants which pass the winter ever green grow well the shade because the shade controls the transpiration of leaves and does not break the balance between the transpiration of leaves and the absorption of roots.
A preliminary information on this subject was made by Nakano, one of the present authors, at the session of the 111 Pan-Pacific Science Congress in 1926. Our present paper aims to demonstrate the previous information gravimetrically, for it was merely based on qualitative observations. For this purpose a tortion balance as well as a vaselining device was used. The results obtained here are summarized as follows: 1. The hydathodes of our fern in question exhibit, so far our observations and experiments concern, no sign of exudation, correspondingly it seems, that it functions exclusively as an absorbing organ. 2. The fern endures its arid state, sometimes even diminution more than 90% of its water content, one month long without showing any indication of damage. 3. The water absorption by the roots of our fern is far less than that by its leaves, and it is quite insufficient by the former only, to balance water deficiency of an arid leaf in nature. 4. By the aid of a gravimetric method, it was distinctly proved, that the water absorption by the leaves of fern depends mainly on the participation of hydathodes, scattered over their upper surfaces, and though in far less degree on that of ordinary epidermis.