The present investigation was made in the course of three years (1961—1963). Thirty-two plots,each of 2—3 mou,in Pinus massoniana stands were selected for esti- mating the fluctuation of population of this serious pest.The estimations comprised of several items,such as sex ratio,fecundity,mortality and others. Based on the results of observations,it was found that in the hilly areas of Kiangsf Province,the outbreak of this pest seemed to be of intermittent epidemic type.The out- break intensity,as measured by the number of generations between two successive out- breaks,varied from 2 to 3 or more generations. The population clensity varied from generation to generation. As a rule, the first generation had the highest population density, and the overwintering generation the low- est. The population density of each generation was mainly decided by the mortality of the first three instar larvae. No close relationship between populations of two successive generations was found. In those areas where there were 2—3 generations a year,the larvae of the second generation when developing to fourth instar,differentiated into two groups.The larvae of the one group went into diapause right away and those of the other continued to de- velop and overwintered as 3rd instar larva in the third generation.The number of larvae in each of the two groups varied with environmental conditions.The ecological significance of this phenomenon should be studied further.But based on the results of examinations,it was found that this phenomenon exerted no influence on the population change of the overwintering generation. Besides the human effect,there were three factors affecting the population changes, namely the climatic,food and natural enemy factors.The effect of climate on popula- tion fluctuation was found to have been greater than that of the food or of the enemies. In Kweichi,Kiangsi,the precipitation in May and in August exerted a decisive effect on the occurrence of outbreak in a year.The food factor affected the population change only in certain localities where the pine needles were completely consummed by this pest. The natural enemies exercised a great effect on the population immediately after the collapse of the outbreak. The number of generations completed in one year varied from the south to the north.There were 3—4 generations in Canton,Kwantung Province,while in Hsinyang, Honan Province only 2—3 generations a year.The highest fecundity was 881 eggs per female with an average of 681.5 eggs.But in general,a female laid only 200—300 eggs.

Melampsora rostrupii Wagner severely infected the seedlings and young trees of Populus tomentosa L,which caused a sharp decreasing in the growth-rate both in length and in width.Generally,the mycelia of the pathogen overwintered in the winter buds, or in the cambium region of the current twigs occasionally.Although the teliospores were existed,yet since no alternate host had been found,that they were of little importance in the occurrence of the disease. Uredospores were produced abundantly on young leaves,leafscars,or infected stems, beginning from the end of March.Such initial infection would soon become an out- break of the disease from May,until the end of September. Uredospores germinated quickly on the back of leaves after inoculated at 19.8— 23.6℃ in 1—2 days at a relative humidity of 100 per cent.However,none or very few spores germinated on the upper surface of the leaf.The development of the epidemic required a monthly mean temperature 18.2—26.8℃,and it would be of little influence when a relative humidity was below 48.1%.Thus,temperature was the main environ- mental factor which influenced the development of this epidemic. Uredinia hypophyllous,scattered or somewhat confluent,roundish,small,1 mm in width;naked when young,somewhat pulverlent,orange-yellow,light-yellow on the oppo- site sides of the pustules,and amphigenous on infected leaves. Uredospores globose,sub-globose or oval,15—22.5×17.5—27.5μ,wall colorless,3μ thick,evenly verrucose with fine papillae;paraphyses capitate or clavate,smooth,50— 75μ long,head 15—23μ broad,wall 3—6μ thick. Telia hypophyllous,sometimes amphigenous,scattered,around the old uredinia,ir- regular roundish,small,1/2—1 mm width,subepidermal,slightly elevated,greyish-brown; teliospous prismatic,1-celled,flat or round at the head,broader in top,7.5—10× 37.5—50μ,light brown,smooth,wall 1—2μ thick. Based on these characters,this fungus is considered to be Melampsora rostrupii Wagner,and it is believed to be the first collection in this country.

The dielectric constants and loss tangents of wood of 16 tree species in the radio frequency region have been measured. Results for the three species,Paulownia fortunei Hemsl.,Picea jezoensis Carr.and Betula albo-sinensis Burk.are presented in some detail.At low moisture content (below 3%),in these species the dielectric constants vary slowly and the maximum values of the various loss tangents occur with the frequency.The curves of 1gσ—1g for the above species are presented as straight lines.The relationship of all specimens between the dielectric constant and density based on the dry wood is in agreement with the Clausius-Mosotti relation.The dielectric values increase with increasing of the moisture content.The dielectric values are the highest in the longitudinal direction,and in the other two directions they are approximately the same.