EXTRUSION OF NUCLEOLI FROM PRONUCLEI OF THE RAT

Electron microscope observations of osmium tetroxide-fixed rat eggs indicate that small nucleoli are extruded from pronuclei in a sharply demarcated time period after sperm penetration. Approximately 4½ hours after sperm penetration, fine fibrous material aggregated in distinct loci along the inner surface of the nuclear envelope and condensed into small, dense bodies. The term tertiary nucleolus or extrusion body is used to designate the forming bodies. The small tertiary nucleoli form distinct protrusions from the pronuclei during the following developmental period and finally bud off into the cytoplasm, carrying with them a small portion of the double nuclear envelope. The extrusion bodies can be observed only in the vicinity of the pronuclei and have not been seen near the cell membrane. The fate of the tertiary nucleoli is not known; apparently they transform or disappear after they have passed into the cytoplasm. Eleven hours after sperm penetration, tertiary nucleoli are not present near the nuclear membrane and the extrusion activity has apparently ceased. Large and small nucleoli react similarly to cytochemical reagents: they are Feulgen negative; they are positive to the Millon, Sakaguchi, brom-phenol blue, and PAS reactions. Azure B stain combined with nuclease extraction indicates the presence of small amounts of RNA in the nucleoli.     

The identification of hybrids ofPhaseolus vulgar is L. ×Phaseolus coccineus L. Using immunoehemical methods

F₁ generace hybrid?Ph. vulgaris L. XPh. coccineus L. je v bílkovinných znacích zhruba intermedierní. V F₂ generaci se objevuje ?těpení a r?zné stupně matro- ?i patroklinity.     

RECURRENT CARCINOMA OF THE RECTUM—Surgical Treatment

Following operations on the rectum for carcinoma, approximately half of the patients have recurrence in the perineum, pelvis, abdomen or at the suture line of anastomosis. The prognosis is almost uniformly poor and although the problems of management are complicated, dealing with them may give the patient worthwhile physical, emotional and economic benefits. Surgical procedures used in the treatment of the common types of recurrence are discussed.     

Consequences of herbivory in the mountain birch (Betula pubescens ssp tortuosa): importance of the functional organization of the tree

Summary Three types of experiments indicate that the functional organization of the mountain birch may influence the ways in which the tree responds to simulated or natural herbivory. The first experiment showed that herbivory to both short and long shoot leaves affects plant development but, because growth largely proceeds by resources of the previous year, is manifested only in the year following the damage. The second experiment showed that even partial damage to a single long shoot leaf caused the axillary bud of that leaf to produce a shorter shoot the next year. Therefore, the value of a leaf depends also on the organ which it is subtending. In the third experiment we manipulated the apical dominance of shoots in ramets and caused improvement to leaf quality in extant shoots. Ramets within a tree responded individually, probably mediated by disturbance of the hormonal control because removal of apical buds elicited the response although removal of the same number of basal buds did not. Induced amelioration is a different response to induced resistance. The two responses are triggered by different cues and may occur in the same plant. By altering hormonal balance of shoots it is potentially possible for herbivores to induce amelioration of food quality. The ways in which herbivory is simulated may explain variability of results obtained when herbivory-induced responses in plants have been studied.     

Phenotypic variation during micropropagation of the chimeralRhododendron ‘President Roosevelt’

The putative periclinal chimeraRhododendron xlimbatum President Roosevelt was used to study the origin of shoots in vitro. Genotypic segregation readily occurred in vitro. Numerous phenotypes were observed, although most shoots were either entirely green or maintained the original variegation pattern. Derivatives of the third apical layer were rarely involved in shoot formation. A reversed chimeral form was isolated. Adventitious shoots were usually miniaturized and rapidly proliferating, but axillary shoots had thicker stems, larger leaves and proliferated more slowly. Corolla tissue produced stunted, leafy shoots; no variegated shoots were produced from floret explants. In shoot tip cultures the addition of 40M 2iP without IBA resulted in the greatest number of shoots. Explant choice was the most critical factor for maintenance of foliar variegation.