DEVELOPMENTAL ANATOMY OF EPIDERMAL AND MESOPHYLL CHLOROPLASTS IN OPUNTIA BASILARIS LEAVES

Developmental studies of Opuntia basilaris Engelm. & Bigel. leaves revealed the presence of three morphologically distinct types of plastids. All epidermal cells examined contained chloroplasts. After 13 days of growth in the dark the plastids of epidermal and mesophyll cells were characterized by the presence of a prolamellar body and fibril inclusions. Epidermal plastids which developed under light conditions contained large stromacentres and a limited grana-fret membrane system. Guard cell plastids developed under similar conditions had a much poorer developed grana system with fibril inclusions apparent only during the developmental stages. At maturity these plastids appeared swollen or dilated. Mesophyll plastids had fibril inclusions during all stages of development and at maturity contained a very extensive grana-fret membrane system. Microbodies were found in association with the mesophyll plastids. Starch accumulation was common in subsidiary cell and guard cell plastids.     

DEVELOPMENTAL ANATOMY IN ROOTS OF IPOMOEA PURPUREA. I. RADICLE AND PRIMARY ROOT

The developmental anatomy of the primary root of Ipomoea purpurea was studied at several growth stages, beginning with the radicle. The radicle is generally composed of three superimposed tiers of initials, which produce the vascular cylinder, cortex, and columella; and a peripheral band of lateral rootcap-epidermal initials. The radicular cortex contains 16–19 immature laticifers; none of the tissue regions in the radicle contains mature cells. Following germination and during the first 2–3 cm growth of the primary root the apical meristem and its derivative tissues undergo a series of modifications. Root apical diameter decreases as cells in lateral portions of the rootcap elongate; meanwhile, the columella enlarges vertically. The relationship between cortical and columellar initials changes as fewer mitoses occur in the former while the latter remain active. In longer roots the columellar initials are directly in contact with the vascular initials. Cortical size diminishes during early root growth as cortical laticifers and their associated cells cease to be produced by the outer cortical initials and ground meristem. Early procambium, at the level of vascular pattern initiation, decreases in diameter by cellular reorientation, and the vascular cylinder decreases in overall diameter although the tetrarch pattern remains unchanged.     

Dormancy in Seeds of Charlock: I. DEVELOPMENTAL ANATOMY OF THE SEED

The anatomy of the embryo, endosperm, and testa throughout thedevelopment of charlock seeds is described. In mature seedsthe embryos are morphologically fully differentiated. Each embryoconsists of a shoot meristem with two large cotyledons but noleaf primordia, and a root meristem with a root cap. The embryois surrounded by a single layer of aleurone-like cells derivedfrom the endosperm and enclosed within the testa. Mucilagesand phenols which could greatly retard the diffusion of oxygeninto the tissues of the embryo are found in the testa. Dormancy,which appears to be induced by a shortage of oxygen, is probablyassociated with the presence of these covering layers.     

DEVELOPMENTAL ANATOMY OF LIGHT-INDUCED ROOT NODULATION BY ZAMIA PUMILA L. SEEDLINGS IN STERILE CULTURE

The developmental anatomy of Zamia pumila L. root apices was studied during light-induced nodulation. Dark-grown roots had an apical organization identical to that of other cycads and similar to that of other gymnosperms. A distinct protoderm was not observed in these roots, which had a large open meristem and a root cap with a well-defined columella. During nodulation, the meristem became reduced in size, and its constituent cells became vacuolate until all but a few resembled ground tissue. The root cap senesced during nodulation, and a recognizable root cap was absent from mature nodules. A file of densely cytoplasmic cells with centrally positioned nuclei developed in the nodule cortex. This layer was continuous across the nodule apex, and was identical to the presumptive algal-zone described previously by other authors. Light-induced nodules branched dichotomously and were identical to algal-free nodules described by other authors. In dichotomously branched nodules, each lobe was covered by a parenchymatous mantle analogous to a root cap. A unicellular layer similar to the presumptive algal zone spanned the gap between opposite nodule lobes, and extended beneath each lobe before terminating in the cortex. Typical meristematic regions were not observed in these nodules. Based on cell sizes and patterns, a meristematic zone was thought to exist between the mantle and the inner cortex.     

THE DEVELOPMENT OF THE SEED OF ABUTILON THEOPHRASTI I. OVULE AND EMBRYO

Winter , Dorothy M. (Iowa State U., Ames.) The development of the seed of Abutilon theophrasti. I. Ovule and embryo. Amer. Jour. Bot. 47(1): 8–14. Illus. 1960.—Abutilon theophrasti Medic, is a widespread annual weed which produces an abundance of seed in capsules which mature within 20 days after pollination. Ovule differentiation may be observed at least 8 days before anthesis when a sporogenous cell becomes evident and 2 integuments are initiated. An 8-nucleate embryo sac is produced from the chalazal megaspore approximately 2 days before anthesis. The outer integument of the mature campylotropous ovule consists of 2 cell layers, the inner integument has 6 to 15 cell layers. The initially free-nucleate endosperm becomes cellular betwen 3 and 7 days after pollination. At maturity a thin layer of gelatinous endosperm encases the embryo. The Asterad-type proembryo of Abutilon has a stout suspensor and develops rapidly. Four days after pollination cotyledons are initiated; 4 days later a leaf primordium is evident. Fifteen days after pollination the embryo, which has essentially completed its growth, consists of a large hypocotyl with root promeristem and root cap at its basal end, and 2 flat, folded, leaflike cotyledons enclosing a small epicotyl at its upper end. The epicotyl consists of an embryonic leaf and a stem apex.     

ROOT ANATOMY OF THE BAMBUSOIDEAE (POACEAE)

Root anatomy was examined for 15 species, in 6 of the 11 tribes of the Bambusoideae. Wide ranges of anatomical variation were found in epidermis, exodermis, cortex, endodermis, pericycle, phloem, xylem, and pith. Although roots of most species seem to resemble the Panicoid type, our study shows much more variation than was described by Goller (1977). These variations could play a role in characterizing taxa within tribes.     

THE COMPARATIVE AND DEVELOPMENTAL MORPHOLOGY OF THE ROOT SYSTEM OF SELAGINELLA SELAGINOIDES (L.) LINK

All of the roots of Selaginella selaginoides are attached laterally to the base of the shoot, which has monopolar growth as is characteristic of Selaginella. The first three roots are produced by meristematic activity in the cortex of the hypocotyl as in several other species of Selaginella. The fourth root is produced in the same way as the first three, except that not all of the cortical cells which become meristematic mature into root tissue. Some of the meristematic tissue remains undifferentiated and continues to produce additional roots. Potentially an unlimited number of roots could be produced, but no plant was found to have more than eight. There is some secondary growth in the cortex of the basal swelling on the hypocotyl, but no secondary vascular tissue is produced and no cambium of any sort is ever organized. On the basis of comparisons with other living species of Selaginella. the centralized root system of S. selaginoides is interpreted as having been modified from a noncentralized type of root system by the persistence of the juvenile mode of root production.     

DEVELOPMENTAL ANATOMY OF SECRETORY CAVITIES IN THE MICROSPOROPHYLLS OF GINKGO BILOBA L.

Two to five secretory cavities develop in the hump region of the microsporophylls of Ginkgo biloba. A developing cavity is first recognized as a spherical pocket of large, densely cytoplasmic cells (central secretory cells) in the median portion of a microsporophyll primordium. These cells degenerate and a small cavity is formed which is filled with the contents of the degenerating cells. Flattened incurved cells (parietal secretory cells) develop around the disintegrating central secretory cells and slough off into the enlarging cavity. Thus, the cavities develop by lysigeny. A mature cavity is surrounded by senescent parietal secretory cells, scanty parenchyma, and a loosely fitting epidermis. Histochemical tests indicate the presence of lipid and pectic substances in the cavities. Previous reports on the morphological interpretation and possible function role of the cavities are discussed in the light of the present investigation.     

COMPARATIVE DEVELOPMENTAL ANATOMY OF SHOOTS OF JUVENILE AND ADULT HEDERA HELIX

Apices of adult Hedera helix have a larger meristematic area, composed of smaller cells, than those of the juvenile shoots. In shoot tips of juvenile plants, cell divisions in the subapical area occur over a longer portion of the shoot, and cell division is continued for a longer period of time. These features are reminiscent of GA-induced changes in other plants. It is suggested that in experiments designed to shift Hedera from the juvenile to the adult form, consideration should be given to agents which affect both rates of cell division and distribution of dividing cells in the young shoot.