Traumatic gum-resin cavities develop in the secondary xylem of the stem of Ailanthus excelsa Roxb. in response to fungal infection and ethephon treatment. After infection or ethephon treatment, traumatic parenchyma in several cell layers develops instead of normal secondary xylem elements. It consists of unlignified axial and ray parenchyma cells. Vessels and fibres are absent. Gum-resin cavities in one or two tangential rows develop in this tissue by the lysis of its axial parenchyma cells. The cavities are bordered by an epithelium. A few layers of traumatic parenchyma cells adjacent to the epithelial cens become meristematic and appear cambiform. The epithelial cells undergo lysis and they evidently contribute to gum-resin formation. As the lysis of epithelial cens proceeds, the adjacent cambiform cens divide to form additional epithelial cells. The process continues for some time and eventually an the axial cells of the traumatic parenchyma break down forming a tangentially anastomosing network of cavities. The cavities do not traverse the ray cells, and the multiseriate rays remain intact like bridges amidst the ramifying cavities.
The influence of two different seasons as well as of thyroid hormone on tail regeneration in Mabuya carinata has been evaluated by measuring the rate of growth of the regenerate at various time intervals. The analysis has revealed no apparent seasonal alteration in the final length attained at the end of 60 days. However, the average per day rate of growth indicates some difference between the late non-breeding and the early breeding phases. A better growth rate was noticeable in the non-breeding phase during the first 25 days (blastemic and differentiation phases) while it was better in the early breeding phase during the last 20 days of tail regeneration (late differentiation and growth phases). These observations correlate with the differential physiological and endocrine status characteristic of the two seasons. Hypothyroidic animals showed a 71% retardation of regenerative ability as compared to euthyroidic animals, which was however rectified by thyroxine replacement. Modes of action of thyroxine on lizard tail regeneration are discussed.