The Development of the Runner-bean Leaf with Special Reference to the Relation between the Sizes of the Lamina and of the Petiolar Xylem: I. The Relation between Lamina Area and Petiolar Xylem

An investigation has been made of the relation between the sizesof the lamina and of the petiolar xylem of both mature and immatureleaves of the runner bean (Phaseolus multiflorus Willd.). The ratios xylem area/lamina area and the number of vessels/laminaarea are lowest for mature leaves. Immature leaves gave higherbut somewhat more variable values for these two ratios. There is a constant growth ratio between the lpminn area andthe xylem area, such that k is approximately o·61 inthe allometry formula. The significance of the results is briefly considered from thepoint of view that the xylem area is related to the water requirementsof the leaf.     

The Development of the Runner Bean Leaf with Special Reference to the Relation between the Sizes of the Lamina and of the Petiolar Xylem: III. The Development of the Leaf under Various Conditions

The development of the first pair of leaves of the Runner Bean(Phaseolus multiflorus Willd.) under various conditions is described. 1. Under damp conditions and also when one leaf of a pair wascovered with a black paper envelope, the rate of developmentwas altered but no significant changes in the relative developmentof the parts of the leaf occurred. 2. Removal of a portion of the lamina at an early stage of developmentresulted, at maturity, in a leaf having relatively less petiolarxylem, although the ratio xylem area/lamina area was slightlyhigher. This treatment also delayed a ‘sudden’ increasein area of the vessels which was seen in normal plants. 3. An attempt was made to estimate the transporting power ofthe petiolar xylem and to compare it with the lamina area. Thedata suggest that the maximum possible area of the lamina atany stage in development may be determined by the transportingpower of the xylem, but that the attainment of this maximumpossible area may be prevented by external factors as is seenin some of the experimental results presented.     

The Transport of Potassium to the Xylem Exudate of Ryegrass: II. EXUDATION

The membrane potentials of ryegrass root cells (E_v0) were foundto be linearly related to the logarithm of the external KClconcentration ([KCl]_o), over the range 0.1 to 20.0 mM. Exudationwas studied over the same concentration range. The concentrationof potassium in the exudate did not vary significantly with[KCl]₀ but the rates of movement of water and potassium to theexudate (f_H2O and f_K respectively) and the electrical potentialand electrochemical potential for potassium in the exudate (E_xoand _x0,K respectively) all tended to decreaseas [KCl]₀ increased. There was a very highly significant correlationbetween f_K and f_H2O. By rapidly increasing [KCl]E₀ and following the depolarization,two components of E_x0 were observed. The first of these wasinstantaneous and was attributed to E_v0 of the epidermal cells.The second component, a gradual repolarisation which commencedabout 9 min later, was attributed to E_v0 of the stelar cells.With an additional contribution from electro-osmosis, thesetwo components quantitatively account for E_x0. The implications of these data for the mechanism of radial iontransport in roots are discussed and it is concluded that thestelar cells are not exclusively specialized for transportingpotassium into the xylem vessels.     

The Tridimensional Morphology of Rice Embryo Development with Special Reference to the Scutellum and the Coleoptile

Using scanning electron microscopy and semi-thin plastic sections, the pattern of development of the rice ( Oryza sativa L. ) embryo from 2 days after pollination (DAP) to maturity was followed. ( 1 ) At 2 DAP, the young embryo was observed to consist of an embryo proper, a hypoblast and a suspensor. The trum-pet-shaped hypoblast was a transitional region situated between the suspensor and the embryo proper. To label the hypoblast as suspensor is incorrect. During this time, dorsiventrality was established, but a radicle was not yet differentiated. Therefore it is still referred to as a proembryo. (2) 3 ~ 5 DAP, the embryo underwent definite morphological and anatomical changes. In the young embryo at 3 DAP the scutellum and colcoptile appeared simultaneously directly from the proembryo. The coleoptile did not originate from the scutellmn. During these foremost 3 days, the coleoptile primordium underwent a special kind of morphological change and formed a young coleeptile having the shape of an inverted hollow cone. This process revealed the true mechanism of c61eeptile formation. Anatomical observation indicated that the embryo at 3 DAP began to differentiate procambium, ground meristem and root cap. At 4 DAP a dome-like growth cone and protoderm of radicle appeared. Then the shoot-root axis became established. At 5 DAP the plumule, hypocotyl and radicle were formed. (3) It was shown that the embryo of rice actually has two cotyledons: the scutellum (a part of the embryonic envelope) and the coleeptile (The scutellum being the lateral cotyledon, a part of outside cotyledon, and the coleoptile the apical cotyledon--the coleoptile may be considered to be a modified form of a cotyledon). This kind of structural arrangemem can be referred to as dimorphic cotyledon.     

The Development and Structure of the Root-nodules of Myrica gale L. with Special Reference to the Nature of the Endophyte

The development and structure of the root nodules of Myricagale are described, and evidence advanced showing that theyrepresent modified lateral roots. Attempts at the isolationof the endophyte were unsuccessful, but on the basis of a cytologicalstudy of the nodules the author adheres to the view of someprevious investigators that the endophyte is actinomycetal.     

The Fixation of Nitrogen associated with the Root Nodules of Myrica gale L., with Special Reference to its pH Relation and Ecological Significance

The paper deals with the fixation of nitrogen by nodulated plantsof Myrica gale under experimental conditions, the fixation being,in the first year of development, of a magnitude comparableto that of legumes under similar conditions. The effect of acidityon the fixation has been investigated. The Myrica organism ismarkedly adapted to acid conditions. The observations are correlatedwith field data in Britain and help to explain the distributionand habits of the species.     

Cytokinin Biochemistry in Relation to Leaf Senescence : II. The Metabolism of 6-Benzylaminopurine in Soybean Leaves and the Inhibition of Its Conjugation

The metabolism of [³H]6-benzylamino purine was studied in presenescent and early senescent soybean (Glycine max [L.] Merr.) leaves. In both types of leaves, the metabolism was essentially the same. The principal metabolite was identified as β-(6-benzylaminopurin-9-yl)alanine by mass spectral studies, which included discharge ionization-secondary ion mass spectrometry and pulsed positive ion-negative ion-chemical ionization mass spectrometry. Conversion to this alanine conjugate was found to be inhibited 2,4-dichlorophenoxyacetic acid and 5,7-dichloroindoleacetic acid.     

Conjugation in Kahlia sp. with Special Reference to Meiosis and Endomitosis

SYNOPSIS. During conjugation of Kahlia the micronuclei divide 3 times before synkaryon formation and 2 times thereafter. The 1st division is heterotypic, as in other ciliates, in that it is characterized by the parachute stage. Following this stage, 24 to 26 bivalents and 4 to 8 univalents appear in the micronuclear area. When the bivalents move to organize the metaphase plate, the univalents lag behind and fail to reach the equatorial region at the same time. Due to this irregular behavior of the univalents there is no distinct metaphase in the first meiotic division. A few meiotic irregularities including the breakdown of the spindle apparatus have been observed. During the breakdown of the spindle apparatus the chromosomes fuse into irregular bodies which resemble the chromosome aggregates observed during the somatic divisions. Generally 1, and rarely more, of the products of the 1st division enter the 2nd division. The spindles of this division are oriented parallel to the long axis of the cell, and 1 of the daughter nuclei reaches the partition membrane separating the conjugants. This nucleus alone undergoes the 3rd division, resulting in the formation of gametic nuclei. Reciprocal exchange and fusion of the gametic nuclei result in the synkaryon formation. The synkaryon divides twice in rapid succession resulting in 4 daughter nuclei; 1 of them degenerates and 2 condense and become functional micronuclei. The chromosomes of the remaining daughter nucleus resemble in size and number the bivalents of the 1st meiotic division. They become polytenic and then reproduce to give rise to the polyploid macronucleus. The development of the macronucleus has been traced from a single diploid set of chromosomes and no evidence has been found for the formation of genetic “subnuclei.” During the early stages of the development of the macronuclear anlage, somatic pairing forces keep the homologs together, while in the later stages these forces cease to exert influence. While these changes are in progress the old macronucleus; breaks up into small irregular polymorphic bodies which are scattered throughout in the cytoplasm. The exconjugants usually encyst and the cysts are not favorable for detailed cytologic study.