The purpose of this paper is to investigate the patterns of root system formation in a plant (tobacco) affected by the soil temperature conditions in a ridge. The experiments were made in (i) unmulched ridge, (ii) mulched ridge and (iii) heated ridge in which heating equipment was buried.
The conclusion from the results of the experiments was as follows:
(1) Root systems in heated ridge had a lot of hard and thick roots and penetrated deep in the soil.
(2) Root systems in unmulched ridge consisted of soft roots and spread over the whole of ridge.
(3) Root system formation in mulched ridge lay between those in heated and unmulched ridges. Thick roots in mulched ridge were seen beneath the surface of the ridge.
(4) Soft and thick roots grew when the temperature in a ridge was low and high respectively.
(5) The patterns of root system were formed in response to the distribution of soil temperature in a ridge.

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Measurement of electric capacitance of plant by high sensitive impedance meter revealed that response of water content in the stem of tobacco plant to step input of environmental elements was similar to that in the stem of cucumber.
It became evident that the information of electric capacitance was equivalent to that of water potential from the relationship between electric capacitance and relative water content of leaf.
Considering from the relationship between dynamic characteristics of electric capacitance and leaf temperature, identification of water content in plants can be performed.
Retardation of transpiration and change in the leaf temperature after the treatment with abscisic acid were made clear by electric capacitance method.

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Leaf temperature measured by infrared thermometer was studied.
Identification of water content in plants by step input of environmental elements was performed by using the information of leaf temperature in addition to the information of electric capacitance.
In the condition of low humidity (for example 50% RH), oscillation in leaf temperature occurred by light input in tobacco plant unlike cucumber.
The cycling pattern of tobacco leaf temperature was the second order lag of S (Laplace transform) and the equivalent time constant was faster in lower relative humidity and in higher temperature.
On the other hand, the response of cucumber leaf temperature was the first order lag of S.
Information of leaf temperature as well as information of water content in plants by means of electric capacitance method could be utilized for monitoring control of plant growth and be indispensable for the optimal control of plant growth.

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To confirm the previous results obtained from the field investigation on viral diseases of tomato plants in greenhouses, eight kinds of genetically different cultivars were mechanically inoculated with common strain of tobacco mosaic virus (TMV-OM), L strain of TMV (TMV-L), cucumber mosaic virus (CMV), and potato virus X (PVX) . The causal factors of necrotic symptom on these inoculated plants were analyzed on the basis of the relationship between the strains of TMV and TMV-resistant genes of tomato plants. Moreover, our attention was focused on the temperature which affects the appearance of symptoms.
With the inoculation of TMV-OM and TMV-L, mosaic symptom accompanied with fern leaf was observed on Fukuju-2 and Ponterosa, susceptible plants. FTVR-50, heterozygous plant of Tm-1 gene, and GCR-237 (homozygous one) were tolerant to both TMV strains. Reiko, heterozygous plant of Tm-1, Tm-2^nv and Tm-2^a genes, and GCR-267, homozygous one of Tm-2^a, were immune to both TMV strains. On the other hand, both TMV strains caused typical necrotic symptom on Ogatazuiko, heterozygous plant of Tm-2^a gene. In the case of GCR-236, homozygous plant of Tm-2^nv, necrotic symptom was observed in 3 out of 8 plants by the inoculation of TMV-L although this cultivar wad immune to TMV-OM. CMV caused fern leaf or mosaic symptom accompanied with fern leaf, and PVX caused mosaic symptom with ringspot in eight cultivars used.
The tomato strain of TMV (TMV-T) isolated from diseased tomato plants with mosaic or necrotic symptom in Shizuoka Prefecture also caused necrotic symptom on Ogatazuiko. Since Reiko was immune to TMV-T isolated from diseased Reiko grafted on BF-101, the necrosis observed on Reiko in the greenhouses seems to be caused by physiological changes in grafting but not by the virus changed in pathogenicity.
Ogatazuiko inoculated with TMV-OM or TMV-L was incubated at 17, 22, and 27°C to confirm whether or not the appearance of symptom on tomato plant having Tm-2^a gene depends on temperature. The necrotic symptom appeared at a temperature higher than 22°C by the inoculation of TMV-OM, but the necrotic symptom appeared at a temperature higher than 17°C by the inoculation of TMV-L.
In control of viral necrotic disease of tomato plants in greenhouses, particular attention must be paid to the selection of immune or tolerant cultivars to the dominantly distributed TMV strain and regulation of temperature.

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