THE RELATION OF AGE AND BUD BREAK TO THE DETERMINATION OF PHYLLOTAXY IN CATALPA SPECIOSA

Catalpa speciosa is interesting in that the phyllotaxy of the lateral shoots can be either decussate or whorled. The pattern appears to be correlated with the number of buds which emerge. The arrangement is not related to dormancy; nor does the stage of development of the bud at the time of bud break influence the phyllotaxy. The control of bud break appears to be related to the position of the bud on the stem. Possible mechanisms controlling the lateral shoot pattern are discussed.     

THE DISTRIBUTION OF APHID INFESTATION IN RELATION TO LEAF AGE

Infestations of apterous Aphis fabae Scop, on potted sugar beets have been followed in detail for several weeks. The plants were somewhat stunted and their crowns presented an unusually complete series of leaf ages. Records were kept of the changing number and size of the leaves and of their stage of growth. Parallel records were kept of the changing population of aphids on every leaf, and the figures are analysed in various ways to show how suitability for the aphids varied through the life cycle of the leaves.
The leaves were very suitable when young, became unsuitable as they matured, became suitable again just after maturity and then unsuitable again as they senesced. But among leaves at any given stage, those which were growing or senescing rapidly were more suitable than those changing slowly, unless the rate of senescence was very high. The differences of population density on different-aged leaves were due largely to the preferences exercised by the apterous adults. The added effect of differences in the fecundity of these mothers while feeding on different leaves was not excluded, but could not be assessed. It is concluded that the physiological development of the plant as a whole determines, through the growth and senescence among its total complement of leaves, the progress and pattern of its aphid infestation.     

RESPONSIVENESS OF YEAST CELLS TO AUXIN, ANIMAL SEX HORMONES AND YEAST SEXUAL HORMONES IN RELATION TO SEX CONTROLLING GENES

Genetic control of the ability of yeast cells to respond to cell-expanding action of animal, plant and yeast hormones was studied. Mating type specificity in the ability to respond to yeast sexual hormones was changed by introduction of homothallism-controlling genes, D and HM. Auxin, a plant hormone can expand cells of most homothallic strains, but not those of heterothallic strains as far as tested. Animal sex hormones showed the action similar to that of yeast sexual hormones.     

水分胁迫对小麦叶片光合作用的影响及其与抗旱性的关系

在水分胁迫初期,两个小麦品种叶片光合速率,气孔导度和细胞间隙CO_2浓度降低,气孔限制值增加,光合速率的降低主要是气孔因素的限制。中度到严重水分胁迫使叶片光合速率、气孔导度和气孔限制值降低,细胞间隙CO_2浓度明显增加,且叶圆片放氧能力,叶绿体Hill反应、叶绿素荧光强度和表观量子产额降低,此时光合速率的降低主要是叶肉细胞光合活性的下降引起的。抗旱性弱的郑引一号叶肉细胞光合活性比抗旱性强的丰抗13更容易受到水分胁迫的影响。     

用体重和体长鉴定黑线姬鼠年龄方法的商榷

在黑线姬鼠种群数量变动的研究中,年龄鉴定是一项重要的工作。分析种群的年龄组成,有助于了解种群的繁殖、生长、死亡和数量发展的趋势。计算不同年龄组所占的比例,更有助于判断某些自然疫源性疾病的流行动态。因此,探讨黑线姬鼠年龄鉴定的方法,有重要的理论与实践意义。     

家蝇中乙酰胆碱酯酶、羧酸酯酶和多功能氧化酶活性与抗药性的关系

本文对几种抗药性和敏感性家蝇品系的乙酰胆碱酯酶(AChE)、羧酸酯酶及多功能氧化酶(MFO)进行了测定.结果表明:①抗药性品系和敏感性品系的AChE活力差异不大, 有机磷抗性品系的AChE对对氧磷的不敏感性比敏感性家蝇明显增大.②某些抗药性家蝇的羧酸酯酶活力比敏感性家蝇大.③抗药性家蝇的MFO活力(O-脱甲基和环氧化)比敏感性家蝇均有不同程度的增高.④二氯苯醚菊酯抗性家蝇对有机磷有负交互抗性.