抄録
The purpose of this paper is to results of observatons on the occurrence of the witche's broom disease of paulownia in the field. Observations were made on about three hundred paulownia trees on the hill of the Fukuoka Prefectural Forestry Experimental station. The trees were planted in 1944. The investigation was continued for five years (1946-1950).
The results of the experiments are summarized as follows.
1. The witche's-broom disease does not attack in groups paulownia trees in the field and is not always transmitted from the infected trees to the nearest healthy ones. So it seems that the occurrence of the witche's-broom of paulownia in the field is not in groups and its process of spreading is not a concentric propagation.
2. The infection ratios are between 10 per cent and 15 per cent in every year and show uniformity statistically within the limit of error of 5 per cent. It seems that the wiche's-broom disease spreads gradually every year at these ratios and it dies not particularly attack young paulownia trees.
3. The root shoots were taken from Chiba, Tokyo and Hozumi districts, and they were divided into three groups by their places of origin. It is recognized statistically that there is uniformity in the infection ratios of the three groups. Therefore, it seems that the infection is not related with the places of origin of the root shoots, if they are paulownia tomentosa species.
4. The field was an inclination of about 10 degrees and paulownia trees were divided into three groups according to the inclinations of the field. It is recognized statistically that there is uniformity in the infection ratios of the three groups within the limit of 5 per cent in both every year observation and the total five years observations. It seems that the infection is not related with the inclination of the field.
5. The paulownia trees were divided into three groups by the breast height circumferrences. It is recognized statistic ally that there is uniformity in the infection ratios. It seems that the infection is not related with the dikgrowth of paulownia trees.
