BIOCHEMICAL CHANGES ASSOCIATED WITH NATURAL AND GIBBERELLIN A3 DELAYED SENESCENCE IN THE NAVEL ORANGE RIND

Several factors associated with senescence of the rind of theNavel orange fruit and their response to GA were studied fromthe time of color change, green to orange, until the fruit passedthe point of any commercial value. This period is typified bya doubling in the concentration of sugar, a decrease in glucoserespiration, and increase in the ratio of K/Ca+Mg. No seasonaltrend could be assigned to O₂ uptake, protein N, total N, orP, Zn, Cu, B, or Na. GA treatment at the time of color changedid not seem to affect these factors until the rind approachedsenescence. At this point, GA effects were observable in theform of higher rates of O₂ uptake, higher rate of glucose respiration,a lag in sugar accumulation, a lower K/Ca+Mg ratio, and a higherlevel of P. These results were interpreted as indicating thatGA maintained a more functional mitochondrial membrane and plasmalemmamembrane. ¹ Paper No. 1768, University of California Citrus Research Centerand Agricultural Experiment Station, Riverside, California,U.S.A.     

ONTOGENY OF THE INFLORESCENCE IN CHENOPODIUM ALBUM

Gifford , Ernest M., Jr ., and Herbert B. Tepper . (U. California, Davis.) Ontogeny of the inflorescence in Chenopodium album. Amer. Jour. Bot. 48(8): 657–667. Illus. 1961.—Chenopodium album, a short-day plant, was induced to flower by subjecting it to successive cycles of 7 hr light and 17 hr darkness. After 4 inductive days, the first macroscopic change is evident in the appearance of precocious axillary bud primordia. After 5–6 days, a primordial inflorescence is visible, and after 7–8 days a terminal flower appears on the main inflorescence axis. The vegetative apex has a biseriate tunica, the cells of which are larger than those of the corpus. The cells of the tunica stain lighter, possess larger nucleoli, and are more vacuolate than cells of the subjacent corpus. After photoinduction, the tunica-corpus organization is maintained, and after 4 short-days, the shoot apex possesses a mantle of 3–4 layers of cells because there are few periclinal divisions in the cells of the outer corpus. The cells of the mantle stain uniformly and are more chromatic than those of the underlying tissue. Mitotic activity was recorded in the upper 40-μ segment of the apex. In the vegetative apex, mitotic activity is greater in the lower portion of the segment. Following photoinduction, mitoses increase throughout the apex until a maximum is reached on the 4th day. Also, the plastochronic interval decreases after photoinduction. Nucleoli of cells of the corpus enlarge following induction until all nucleoli of the apex are nearly equal. Included in the paper are discussions of the general morphological differences between vegetative and flowering shoots.     

ONTOGENY OF FOLIAR DIAPHRAGMS IN TYPHA LATIFOLIA

Morphogenetic pulsations in the intercalary meristem of the leaf of Typha latifolia (Typhaceae) produce regular alternating sequences of vascular and stellate-celled diaphragms separated at first by rib-meristem derivatives. The collapse of these derivatives in the region of elongation in and above the intercalary meristem, and the separation of the diaphragms from each other, produce a mature compartmentalized leaf, the compartments bridged by porous diaphragms but separated from each other by rigid vascularized partitions.     

ONTOGENY OF ALEURONE GRAINS IN COTTON EMBRYO

Cotyledon mcsophyll cells in maturing seeds of Gossypium hirsutum from aleurone grains by accumulation of protein and other materials in vacuoles. Globoids and unidentified, electron-dense particles can be found in the matrix of amorphous protein. As revealed by electron microscopy, the vacuoles appear to communicate with cisternae of endoplasmic reticulum in early stages of development. This paper and many reports in the literature cast doubt on the reported plastid nature of certain aleurone grains.     

ONTOGENY OF FOLIAR VENATION IN EUPHORBIA FORBESII

Six species of Euphorbia endemic to the Hawaiian Islands have disjunct veins as a normal component of their foliar anatomy. An ontogenic study of the foliar venation of one of these species, E. forbesii, showed a normal development of the foliar procambium as determined by previous studies of dicotyledonous leaves. The disjunct veinlets are isolated early in the histogenesis of the intersecondary veins when certain procambial cells fail to differentiate into vascular tissue. It appears that these cells develop into normal parenchymatous cells of the ground tissue. It is suggested that these cells are physiologically distinct from the rest of the procambial cells. In no instance was a tracheary element seen which appeared to have arisen independently of the normal procambial reticulum.     

ONTOGENY AND DIFFERENTIATION OF SCLEREIDS IN RAUWOLFIA

An interesting anatomic feature of Rauwolfia is the occurrence of a remarkable type of sclereid in the stem and root. The initials of the sclereids in the stem arise in the ground tissue element of the pith in a region between 50 and 70μ below the surface of the shoot apex. This region of the shoot remains surrounded by a whorl of either 3 or 4 leaves. Sclereids initiate in succession in association with each whorl of leaves. Thus, the sclereids are restricted to the nodes. The sclereids in the stem arise as a primary element of the shoot from the ground tissue of the pith. In the root, they differentiate from the cells of the phelloderm and are secondary in origin. Morphologically, the sclereids in these 2 organs are basically the same, except that the sclereids in the stem are larger in size than those in the root. A solitary cell, or 2 to several cells in a longitudinal cell file (originated from a single mother cell), may differentiate into sclereid initials. The growth of the sclereids through relatively compact ground tissue of the pith is possibly accomplished by a combination of gliding growth and apical intrusive process. The sclereid initials grow rapidly and force their way between the parenchymatous cells. As a result, the neighboring cells lose their original surface contacts. Sclereids increase in size rapidly, and, therefore, very enlarged sclereids with thin primary walls may be observed in the second node. They mature progressively in basipetal direction in the subjacent nodes. In the fifth or sixth node, mature sclereids with massive secondary walls are most common. The secondary walls of sclereids contain much lignin as determined by the phloroglucinol-HCl test. The walls of sclereids at maturity show a variable number of lamellae ranging from 10 to 15 in the lateral walls. A remarkable feature of the sclereids is their canal-like pits in the secondary walls. Two adjacent pits may coalesce uniquely to form a Y-like configuration directed centrifugally from the lumen of the sclereids. The sclereids are ventrically symmetrical, joined end-to-end by their transverse walls like 2 superimposed young fibers.     

ONTOGENY OF THE TENDRIL IN VITIS VINIFERA

The apical meristem of the grape tendril possesses several remarkable features: bilateral symmetry, a minimal number of appendages, and an exceedingly brief period of apical meristem activity. The cellular configuration of the apex changes from tunica-corpus to zonate, as rudimentary leaves and branch-tendril apices are initiated. Eventually the apical meristem of the tendril itself ceases meristematic activity and differentiates as a large hydathode. Typical spongy epithem tissue, copious xylary tissue, and water-pores in the epidermis characterize the hydathode. Numerous vascular strands traverse the length of the tendril and terminate in enlarged tracheary elements adjacent to the epithem. Cessation of meristematic activity follows lowered mitotic rate in the summit and accelerated differentiation below and within the meristem.     

ANATOMICAL CHANGES DURING LEAF ONTOGENY IN POPULUS DELTOIDES

The leaf plastochron index (LPI) was used to interpret the anatomical changes during leaf ontogeny in the developing leaf zone of young cottonwood trees and to relate leaf anatomical structure to physiological function. The lamina tip matured precociously with respect to both structure and function. Below the lamina tip the intercellular spaces, stomates, and minor veins matured basipetally, while the major veins developed acropetally. Ontogenetically, maturation progressed from LPI –1.0, which was anatomically immature except for its lamina tip, to the first fully expanded leaf at LPI 6.0, which was anatomically mature. Physiological maturity also occurred at LPI 6.0, thus signifying a transition with respect to both structure and function. By evaluating the anatomical observations in conjunction with physiological data collected at comparable LPI's in other experiments, it could be demonstrated that anatomical development was a limiting factor in photosynthesis and translocation of assimilates.     

KINETIN MODIFICATION OF SPORELING ONTOGENY IN MARSILEA VESTITA

Laetsch , W. M., and Winslow R. Briggs . (Stanford U., Stanford, Calif.) Kinetin modification of sporeling ontogeny in Marsilea vestita. Amer. Jour. Bot. 48(5): 369–377. Illus. 1961.—Sporelings of the fern, Marsilea vestita Hook. and Grev., were cultured aseptically with a wide concentration range of kinetin. The elongation of the primary and all succeeding roots was significantly inhibited by concentrations as low as 0.3 γ/l., and was almost completely inhibited at concentrations above 30 γ/l. Root inhibition by kinetin was a result of decreased cell division and was not influenced by the amount of available carbon in the medium. The primary leaves also were inhibited by kinetin, but only by higher concentrations. The relative numbers of organs present were altered by intermediate concentrations, with a rise in the number of roots per plant, and a corresponding decrease in the number of leaves. Sporelings maintained in these kinetin concentrations for long periods developed abnormal leaves and roots. The shoot apex lost its organization in higher concentrations and proliferated into callus. The histology of the callus is discussed. The kinetin effects were independent of light conditions. Various other growth-active compounds were studied in combinations with each other and with kinetin for their effects upon sporelings. Interactions between these compounds were not apparent, and they neither substituted for nor modified the effects of kinetin. The use of kinetin as a tool in morphogenetic study is discussed.     

COMPARATIVE ONTOGENY OF THE PERIANTH IN MIMOSOID LEGUMES

Comparative ontogeny of the perianth is reported for representative genera and species among mimosoid legumes in order to elucidate intertribal relationships and also relationships to the other two subfamilies of legumes. Initiation of the perianth is acropetal in two whorls. The calyx arises first followed by the corolla. Order of initiation of both calyx and corolla is determined during early ontogeny. Four different types of order of initiation have been found in the calyx: helical, simultaneous within one whorl, bidirectional, and ring meristem. Helical initiation is considered primitive; simultaneous within one whorl, bidirectional, and ring meristem are considered derived. Differences during early organogeny in the calyx among mimosoids result in similar morphologies of the mature calyx which indicates that parallel evolution may have played a major role in evolution of radial symmetry within the group. Order of initiation of the corolla is uniformly simultaneous whorled with one exception. Position of organs is a significant feature which separates mimosoids from caesalpinioids and papilionoids. In mimosoids the median sepal is located abaxially and the median petal adaxially in relation to the subtending bract. In both caesalpinioids and papilionoids the median sepal is located abaxially and the median petal adaxially in relation to the subtending bract. Fusion of the calyx in some taxa can be interpreted as an example of acceleration.     

ONTOGENY OF THE FOLIAR SCLEREIDS IN NYMPHAEA ODORATA

Gaudet, John. (U. Rhode Island, Kingston.) Ontogeny of the foliar sclereids in Nymphaea odorata . Amer. Jour. Bot. 47(7): 525–532. Illus. I960.—The “diffused” idioblastic sclereids develop in the leaves of Nymphaea odorata Ait. during periods when leaves are forming on the shoot apex, and they are initiated by cells which are differentiated from other cells of the fundamental tissue by nuclear size. The ontogeny of the sclereids is similar in most cases, but differences are apparent among petiolar, laminar and stipular types, especially, when the adult morphology is considered. At maturity, the sclereids are usually pitted in the central portion, and they do not show “polarity” in the leaf or orientation near the tracheary elements, which occur in the same tissue. The “spicule-like” protuberances and the angular cross-sectional shape of the stipular sclereids are interpreted as evidence that growth of these sclereids was restricted as compared to other types of sclereids which were not restricted.