Studies on the rosette plant Hieracium floribundum.: I. Observations related to flowering and axillary bud development

Hieracium floribundum is a rosette species requiring a number of long days for flower induction. Histological studies of vegetative, transition, and floral apices showed the structural changes associated with flower induction in this species. One striking histochemical change observed was the absence of starch in vegetative apices and the accumulation and retention of quantities of starch in prefloral and floral apices. A study of initiation and development of axillary buds at the time of flowering revealed that there was a gradient in the potential to flower shown by these buds along the developing flower stalk to the base of the plant. The buds in the axils of upper peduncle bracts always develop as capitula while the apices of the buds in the axils of the next few bracts assume the shape of floral buds but fail to develop unless the upper developing inflorescences are removed. Buds in the axils of the lowest bracts and upper (youngest) leaves have the potential to form rosettes, stolons, or inflorescences depending on the environmental conditions in which the plants are grown. Buds formed in the lower (oldest) leaf axils normally fail to grow out until after seed set when a few may develop as rosettes. Possible explanations for these results are discussed, and some experimental approaches being used to elucidate the physiological basis for bud expression are indicated.

HISTOCHEMICAL OBSERVATIONS ON THE GRANULOSA AND THECA INTERNA DURING FOLLICULAR DEVELOPMENT AND CORPUS LUTEUM FORMATION AND REGRESSION IN THE AMERICAN OPOSSUM

SUMMARY A study has been made of the histochemical changes which occur during follicular growth and formation and regression of the corpus luteum in the ovary of the American opossum. The granulosa cells show abundant cytoplasmic RNA. Some lipid bodies consisting of phospholipids are sparsely distributed among the granulosa cells. After ovulation, the granulosa cells undergo 'luteinization' to form the large luteal cells. The most striking histochemical change involved in the differentiation (or luteinization) of the granulosa follicle cell into a luteal cell is the development of abundant diffuse lipoproteins throughout the cytoplasm. Fine lipid granules consisting of phospholipids are also formed in the cytoplasm of luteal cells. The stromal elements of the theca interna, which contain some sparsely scattered phospholipid granules, do not show any histochemical change during corpus luteum formation. With the regression of luteal cells, coarse lipid granules consisting of cholesterol and cholesterol esters, triglycerides and some phospholipids accumulate abundantly in the cytoplasm. Some of these regressing luteal cells continue to persist in the ovarian stroma for some time.

LARYNGOTRACHEITIS VIRUS IN CHICKENS

Infectious laryngotracheitis can be produced in chickens as an experimental model of severe nonfatal rhinitis and sinusitis. Inoculated intranasally into unanesthetized baby chicks it remains limited to the nasal fossa, produces acute desquamation of all nasal epithelia, results in functional recovery of the respiratory epithelium, but leaves important residual abnormalities. From the earliest recognizable lesions through 4½ months' convalescence, the principal changes are as follows: 1. Initial lesions, or small syncytia of intranuclear "inclusions", first identifiable in the mucociliated cells of the shallowest portion of the epithelium at about 21 hr postinoculum (the inner surface of the maxillary conchal scroll). 2. Acute sloughing, (about 3 to 7 days), marked by: (a) spread of lesions from cell to cell via multinucleated "giant cells" which progressively slough and desquamate respiratory, olfactory, and sinus epithelia, epithelial neural elements and blood vessels; (b) appearance of numbers of eosinophilic leukocytes along the basement membrane at the sites of lesions just previous to sloughing; intensive infiltration of the submucosa with small lymphocytes after sloughing begins; (c) histochemical change in the intracellular mucus of the cells which comprise the syncytia: this mucus stains with Alcian blue alone when stained with AB-PAS; and (d) all cartilages of the maxillary conchae become flaccid, and the cell nuclei and matrix lose both basophilic and Alcian blue staining properties, effects which recede by about the 8th day. 3. Repair (about 8 to 21 days), marked by rapid initial spread of a sheet of epithelial cells over the infiltrated subrmucosa, appearance of numbers of plasma cells circulating in the tissues, formation of encapsulated secondary nodules, and mucosal adhesions. 4. Convalescence (about 1 to 4½ months when experiments terminated), marked by functional restoration of the mucociliary lining of the nasal fossa. However, at 4½ months eight specimens all show complete metaplasia of the olfactory organ (end nerves, supporting cells, and glands of Bowman) to mucociliated epithelium, all show abnormal formation and alignment of mucous acini, and about 50% have severe persistent sinusitis.