THE HYDRATED MEGASPORE OF MARSILEA VESTITA

The megaspore of Marsilea has an exospore composed of several layers and is contained within the original megasporangial wall (making it technically a megasporangium). Upon contact with water there is an almost explosive unrolling of the megasporangial wall and expansion of the spore wall layers into a complex structure, part of which has not been previously described. The dynamics of the hydration process and the resultant structures are described.     

THE DEVELOPMENT OF THE SPOROCARP OF MARSILEA VESTITA

The tissues of the sporocarp of Marsilea vestita undergo profound changes during development. Early in development, the cells of the peripheral tissues, epidermis, hypodermis and layers of the transitional zone between the hypodermis and more internal tissues contain prominent vacuolar bodies. As development proceeds, these vacuolar bodies disappear. Prominent amyloplasts are found only in the guard cells and in the cells of the transitional zone. Later in development the cells of the hypodermis divide periclinally forming two layers which differentiate as macrosclereids. The cells of the outermost layer of the transitional zone differentiate as osteosclereids. Internally, the cells of the sorophore accumulate large amounts of mucilage in the central vacuoles. The peripheral cytoplasm ultimately degenerates leaving just hygroscopic mucilage. The mucilage carbohydrate contains the sugars, rhamnose and arabinose. In the young sorus, only the spore mother cells and the cells of the indusium contain amyloplasts. By the time of meiosis, there is a massive accumulation of starch in the receptacle, stalk and jacket but not in the tapetum of the sporangia. Late in development, the starch disappears and the mega- and microspores become coated with carbohydrate.     

MORPHOLOGY OF MARSILEA VESTITA. I. ONTOGENY AND MORPHOLOGY OF THE SUBMERGED AND LAND FORMS OF THE JUVENILE LEAVES

During their ontogeny, the primordia of the juvenile leaves of Marsilea plants in sterile culture develop 1, 2 or 4 marginal meristems, and these, in turn, contribute cells to the young leaf by anti- and periclinal cell divisions. The final leaves are unifid, bifid, or quadrifid, depending on how many marginal meristems develop, and this is determined early in the ontogeny of the leaf. The mechanism which determines whether or not a marginal meristem develops may fluctuate, as shown by the existence of trifid leaves. Two forms of juvenile leaves are produced, those in a liquid medium, which in many respects resemble the adult quadrifid submerged leaves, and those on a solid medium, which in many respects resemble the adult land leaves.     

MITOTIC ACTIVITY IN THE ROOT APEX OF THE WATER FERN MARSILEA VESTITA HOOK. AND GREV.

Roots of Marsilea vestita ranging from 1–120 mm in length, as well as root primordia, were analyzed to determine mitotic activity and ploidy levels in the apical cell, five well-defined regions of the root proper, and two regions in the root cap. The mitotic index of the apical cell tended to be above the overall mean mitotic index for the entire apical meristem. No diurnal rhythm in mitotic index was apparent. The cell-cycle duration of the apical cell ranged from 12.1–25.2 hr, that of other regions of the root from 16.1–41.5 hr. There was no indication of polyploidy in any part of the apical meristem except in a few procambial cells. Thus, the results support the classical concept that the apical cell is the ultimate source of cells in the root.     

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 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 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.     

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.     

ONTOGENY OF THE ULTRADIAN RHYTHM OF ACTIVITY IN JAPANESE QUAIL

As soon as they hatch, gallinaceous chicks follow broody hens. This matriarchal unit presents a temporal organization of activity. The ontogeny of this ultradian rhythm of activity was followed in Japanese quail during their first 3 weeks of life. Under controlled laboratory conditions, 12 groups of four chicks were recorded using an activity monitoring system. They were observed between the ages of 2 and 17 days. Chicks in groups presented an ultradian rhythm of activity, with a period that increased significantly from 14.3 ± 1.4 minutes when chicks were 2 days old to 26.0 ± 1.9 minutes when they were 16 days old. The increase of ultradian periodicity was particularly pronounced during their first and third weeks of life. Finally, the ultradian period was correlated positively with body weight of the chicks. (Chronobiology International, 17(6), 767–776, 2000)     

A NEW SPECIES OF MARSILEA FROM THE DAKOTA FORMATION IN CENTRAL KANSAS

Discovery of compression/impression megafossil material from the Cenomanian (mid-Cretaceous) in Kansas documents the occurrence of the genus Marsilea during this age. Only vegetative material has been found as complete plants; associated structures that may be fertile structures could belong to the genus also. This new fossil species extends the megafossil record of the genus back to the mid-Cretaceous when previously only megaspores attributed to the family occurred during this time. The fossil record of the heterosporous aquatic fern families is reviewed with emphasis on the Marsileaceae.     

ONTOGENY AND STRUCTURE OF THE SECONDARY PHLOEM IN EPHEDRA

The secondary phloem in Ephedra is atypical of the gymnosperms in general and exhibits several angiosperm-like characteristics. The ray system of the conducting phloem consists of parenchymatous, multiseriate rays. The axial system contains parenchyma cells, sieve cells, and unusual albuminous cells reminiscent of the specialized parenchyma cells found in some angiosperms. These cell types may intergrade with each other. P-protein in the developing sieve element appears early in the form of a single, ovoid slime body. Later, smaller slime bodies appear and quickly disperse. In the mature sieve element the single, ovoid slime body is lost, and P-protein is then evident in the form of a parietal cylinder, thread-like strands, amorphose globules, or a slime plug. Necrotic-appearing nuclei are commonly found in mature sieve cells.