THE INFLUENCE OF GROWTH SUBSTANCES ON THE INDUCTION OF APOGAMY IN PTERIDIUM GAMETOPHYTES

Experiments employing sequences of three media demonstrated the effect of growth substances on the induction of apogamy. The most effective sequence was 4% sucrose 1–14 days, 4% sucrose plus growth substance 15–28 days, and 0.1% sucrose 29–56 days. In this sequence concentrations of NAA, IAA, and GA promoted apogamous shoot formation. A higher NAA concentration than optimal for shoot formation stimulated apogamous root formation in all medium sequences. Kinetin was without effect or inhibitory to apogamy. Combination of kinetin/GA or GA/NAA concentrations did not increase the apogamous response. One combination of the kinetin/NAA concentrations had a synergistic effect on the apogamous shoot formation. Additions of GA to the synergistic kinetin/NAA combination had an antagonistic effect on the apogamous response.     

THE INITIATION OF SPOROPHYTES BY OBLIGATE APOGAMY IN CHEILANTHES CASTANEA

The initiation of apogamous sporophytes in Cheilanthes castanea was recorded by daily photography of individual gametophytes. Whereas an ordinary embryo arises from a zygote, apogamous embryos of C. castanea originate from one to three initial cells which occur just behind the apical region of the prothallus. The initial (or initials) produce cells with small chloroplasts behind the sinus of the gametophyte. The appearance of cells with smaller chloroplasts than those normally found in gametophytes is the first indication that apogamy is occurring. The cells with small plastids produce a group of densely-cytoplasmic meristematic cells. The size of the meristematic mass increases until shoot and root apices of the apogamous embryo are organized.     

TRANSLOCATION OF 14C IN MACROCYSTIS INTEGRIFOLIA (PHAEOPHYCEAE)1,2

Translocation patterns in the giant kelp, Macrocystis integrifolia Bory, were investigated in situ using ¹⁴C tracer; sources and sinks were identified. Export was first detected after 4 h of labeling; experiments were routinely 24 h continuous ¹⁴C application. Mature blades exported ¹⁴C to young blades on the same frond and on younger fronds, as well as to sporophylls and frond initials at the bases of the fronds. Blades <0.3 m from the apex imported and did not export; this distance did not change seasonally. In spring export from blades 0.3–1.25 m from the apex was exclusively upwards; older blades also exported downwards. In fall downward export began 0.5 m from the apex, and blades >2 m from the apex exported exclusively downwards. Carbon imported by frond initials, young fronds, and sporophylls in fall may partly be stored for growth in early spring. No translocation was seen in very young plants until one blade (secondary frond initial) bad been freed from the apical blade; this blade exported to the apical blade for a time, but imported when it began to develop into a frond. The second and third formed blades on the primary fronds (sporophylls also exported when <0.3 m from the apex, and later stopped. Frond initials and sporophylls on later-formed fronds did not export at all. The translocation pattern in M. integrifolia differs from that previously reported in M. pyrifera in seasonal change and in distances from the apex at which the changes take place.     

水稻多卵卵器的起源

被子植物的卵器中通常只有１ 个卵细胞。在水稻（Ｏｒｙｚａ ｓａｔｉｖａ）多胚品系胚囊中观察到二卵卵器和三卵卵器。对其大孢子和胚囊发生进行了观察,首次揭示了被子植物多卵卵器的起源。该品系大孢子发生正常。大孢子母细胞进行正常的减数分裂形成４ 个大孢子。靠近合点端的大孢子发育,其它３ 个退化。功能大孢子第一次有丝分裂后,两个子核被一中央大液泡分隔在胚囊珠孔端和合点端。紧接着发生第二次有丝分裂,合点端核分裂时纺锤丝与胚囊纵轴平行,而珠孔端核分裂时纺锤丝与胚囊纵轴成４５°夹角。由此产生的四核胚囊中,合点端１核向胚囊中部或中上部（胚囊珠孔端）迁移。四核胚囊再经１ 次有丝分裂形成两种类型的核分布偏离蓼型的八核胚囊。一种类型是珠孔端４个核,中部与合点各２ 个核,在胚囊细胞化过程中,珠孔端４ 核分化成四细胞卵器,其中卵细胞和助细胞各２ 个,中部的２ 核分化成２ 极核中央细胞,合点端的２ 核形成反足细胞。另一种类型是珠孔端６ 个核,合点端２ 个核,在胚囊细胞化过程中,两端各１ 核向中部迁移分化成２ 极核中央细胞,珠孔端剩余的５ 核分化成５ 细胞卵器,其中卵细胞３ 个,助细胞２ 个,合点端的１ 核迅速分裂形成反足细胞     

APOGAMY AND SOMATIC RESTITUTION IN THE FERN CERATOPTERIS

A mutant stock of the fern Ceratopteris has been derived from an inbreeding study following an interspecific hybridization between two diploid species. The mutant is characterized by gametophytes that produce non-functional spermatozoids and are incapable of selfing. Sporophytes develop apogamously from the mutant gametophytes and, although they are initially haploid and sterile, portions of the fronds later become doubled somatically and behave like tissues of sexually derived homozygous sporophytes. The mutant segregates from sporophytes in a 1:1 ratio when crosses are made with wild type gametophytes. Certain aspects of the behavior are similar to those seen in some naturally occurring apomictic ferns.     

INDUCTION OF ANTHERIDIA IN ASCOBOLUS STERCORARIUS

Sexual organs develop in the hermaphroditic, heterothallic ascomycete Ascobolus stercorarius only when strains of opposite mating-type are paired under appropriate conditions. A previous study of the two reciprocal compatible interactions, A-antheridial/a-ascogonial and a-antheridial/A-ascogonial, revealed several differences between them. The present study of the induction of antheridia has uncovered several other differences. Such induction occurred on severed hyphae, non-germinated oidia and germinated oidia of mating-type A but not of a under two different sets of conditions: (1) when such elements were placed on an agar medium containing only the secretions of a compatible mycelium, and (2) when they were in close proximity to a second group of compatible non-germinated or germinating oidia on an agar surface. This tendency for vegetative elements of A to differentiate as male structures more readily than those of a is consistent with the previous observation that the interaction of A-antheridial/a-ascogonial is generally the more vigorous one. It may also be responsible for a condition approaching functional sexual dimorphism in many mixed (A + a) mycelial cultures.     

PATTERNS OF ALLOZYME DIVERSITY IN THE WEST INDIES CYCAD ZAMIA PUMILA (ZAMIACEAE)

The West Indies cycad, Zamia pumila, is restricted to the Greater Antilles, northern Bahama Islands, Florida, and the southeastern coast of Georgia. An electrophoretic study based on nine enzymes compared 21 accessions from throughout the range of the species. Lower levels of intrapopulation variation than those reported for ferns, other gymnosperms, and angiosperms were discovered for the two more extensively sampled populations. However, this variation was similar to that found in other island taxa and in the endemic Australian cycad, Macrozamia communis. In contrast, allozyme divergence among accessions of Z. pumila appeared relatively high, mostly as a result of rare alleles restricted in geographic distribution. The age and biogeography of Z. pumila may gave contributed to population differentiation. Also, mean number of alleles per locus was low for the species (1.75). Finally, the time-since-divergence value (10.8 million years ago) between Z. pumila and its closest extant relative, Z. splendens, was much smaller than the age of Z. pumila suggested by the fossil record and historical geology of the Caribbean (30–60 million years ago). Together, these data indicate that biochemical evolution within this species, and perhaps in all cycads, is slow when compared to that of noncycad seed plants.     

INTRAPOPULATIONAL VARIATION IN LEAFLET MORPHOLOGY OF ZAMIA PUMILA L. IN RELATION TO MICROENVIRONMENT AND SEX

The cycad Zamia pumila L. was examined for differences in leaflet morphology between sun and shade plants and between males and females within a single population in northern Puerto Rico. Sun leaflets are significantly smaller than shade leaflets in length, width, and surface area; and sun leaflets have a higher length: width ratio than shade leaflets. Also, average densitythickness is greater for sun leaflets than for shade leaflets. Males and females are similar in leaflet size; but the females had a larger number of leaflets per leaf than males.     

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.     

INDUCTION OF XYLEM ELEMENTS IN ISOLATED COLEUS PITH

Small pith explants from the fifth internode of Coleus blumei were placed on a defined medium supplemented with different concentrations of indoleacetic acid (IAA). With all levels of IAA tissue growth was slight; however, when the medium contained more than 10^-7 m IAA, xylem elements developed after 11-14 days. Omission of sucrose from the medium prevented this differentiation of xylem elements. Isolated xylem cells or small nodules were most common, but long strands were also seen. The merits of the Coleus system for study of plant-cell differentiation are discussed.     

INDUCTION OF WOUND-VESSEL DIFFERENTIATION IN ISOLATED COLEUS STEM SEGMENTS IN VITRO

Excised internodes and 2-mm-thick transverse stem segments of Coleus blumei were incubated 7 days on media containing 2% sucrose, 1% agar, and various growth substances. Wound-vessel members differentiated in the 2-mm-thick tissue slices incubated on medium containing no exogenous auxin (control). Compared to control slices, the addition to the medium of either IAA (50 or 5 ppm), 2, 4-D (10, 1, or 0.1 ppm), TIBA (50, 5, or 0.5 ppm), or kinetin (50, 5, 0.5 or 0.05 ppm) inhibited wound-vessel differentiation. Simultaneous treatment of tissue slices with IAA and kinetin inhibited wound-vessel differentiation, as did the incubation of tissue slices on medium containing no sucrose. Low concentrations of IAA (0.05 ppm) or 2, 4-D (0.01 ppm) resulted in over a 100% increase in the numbers of wound-vessel members differentiated. These results are interpreted as indicating auxin synthesis by the tissue slices and the participation of auxin as a limiting factor in xylogenesis. The inhibition of wound-vessel differentiation by relatively high concentrations of 2,4-D, TIBA, or kinetin is interpreted as a reflection of the inhibition of polar auxin transport by these substances, and an indication that polar auxin transport enhances xylogenesis.