摘要:

The shoot apex ofTriticum aestivumcv. Ramona 50 was investigated histologically to describe cell lineages and events during leaf initiation. During histogenesis three periclinal divisions occurred in the first apical layer, with one or two divisions in the second apical layer. This sequence of cell divisions initially occurred in one region and spread laterally in both directions to encircle the meristem. Cells of the third apical layer were not involved in leaf histogenesis. Initially, young leaf primordia were produced from daughter cells of periclinal divisions in the two outer apical layers. Nuclear contents of protein, histone, and RNA in the shoot apex were evaluated as ratios to DNA by means of semiquantitative histochemistry. Daughter cells of periclinal divisions in the outer apical layer which produced the leaf primordia had higher histone/DNA ratios than cells of the remaining meristem. However, protein/DNA and RNA/DNA ratios were similar in both regions. Leaf initial cells had a higher3H‐thymidine labeling index, a higher RNA synthesis rate, and smaller nuclear volumes than cells of the residual apical meristem.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10174.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

Seeds of the winter annualViola rafinesquiiGreene exhibit true dormancy at the time of maturity and dispersal in mid to late spring. During the summer rest period the seeds pass from a state of true dormancy to one of relative dormancy and finally to what may be called a state of complete nondormancy. As the seeds enter relative dormancy they will germinate mostly at relatively low temperatures (10, 15, 15/6, and 20/10 C), but as after‐ripening continues they gain the ability also to germinate at higher temperatures (20, 25, and 30/15 C). During June, July, and August seeds will not germinate at field temperatures even if kept continuously moist. But by September and October seeds may germinate to high percentages over a wide range of temperatures, including September and October field temperatures. This pattern of germination responses, involving breaking of true dormancy and widening of the temperature range for germination during relative dormancy, appears to be an adaptation of the species to a hot, dry season. Seeds ofV. rafinesquiistored on continuously wet soil (field capacity) or on soil that was alternately wet and dried during the summer did not after‐ripen at low temperatures (10, 15, 15/6, and 20/10 C) but did after‐ripen fully at high temperatures (20, 25, 30/15, and 35/20 C). Thus, the high temperatures thatV. rafinesquii“avoids” by passing the summer in the dormant seed stage actually are required to break seed dormancy and, therefore, are essential for completion of its life cycle.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10175.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

A hypothesis in the literature suggests that apical size is one of the critical determinants of the number of organs a flower will form. Genetically selected and control lines ofLinanthus androsaecusssp.androsaecus(Polemoniaceae) were used to test this hypothesis. Plants in the selection up (SU) line of this species produce flowers with greater than the normal number of corolla lobes, and plants in the selection down (SD) line produce less than the normal number of corolla lobes. Apices from lateral branches collected from plants just prior to flowering differed in size among these two lines and controls. Plants in the SU line showed an increase in apical diameter in median section while plants in the SD line showed a decrease in apical diameter in comparison to controls. SU plants may be flowering later, and SD plants earlier, than controls. SU and control apices from the main stem, collected from plants in a late stage of vegetative growth, also differed in apical diameter. Increase in the number of apical cells is associated with increased size in SU apices in comparison to controls. Apical size differences associated with petal number appear to become established during vegetative growth by the time the first two pairs of foliage leaves are formed. The selected and control lines ofL. androsaecusoffer support for the hypothesis that apical size is an important factor in the determination of petal number.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10176.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

Numerous specimens of the pteridospermous pollen organsIdanothekion glandulosumandCallandrium callistophytoidesare present in Middle and Upper Pennsylvanian petrifaction material, respectively. Several specimens ofIdanothekion, previously known only in an isolated condition, are attached to foliage assignable to the monostelic seed fernCallistophyton. Proof of the affinities ofIdanothekionallows this genus to be elevated from a form genus to an organ genus in the Callistophytaceae. The structure of the foliage and the mode of attachment of theIdanothekionspecimens are like those previously described forCallandrium. Structural features ofIdanothekionandCallandriumare compared, and the question of their identity is discussed. At present one basic type of pollen organ, borne on the abaxial surface of foliar pinnules, is known for members of the Callistophytaceae.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10177.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

InCordyline terminalisnegatively geotropic leafy shoots and positively geotropic rhizomes develop from single axillary buds on either shoots or rhizomes. All axillary buds have similar morphogenetic potential when released from apical dominance. Experiments in which the orientation of the apex is changed, organs removed, or growth regulators applied indicate that after a rhizome is initiated, it is maintained as a rhizome by auxin originating in the leafy shoot. When auxin levels are lowered by changes in the orientation of the axis or shoot removal, the rhizome apex becomes a shoot apex, which appears to be the stable state of the actively growing apex. Benzyl adenine when applied exogenously to the apex or lateral buds has the same effect as lowering the auxin level. Gibberellic acid has no effect on the apex or lateral buds. High levels of exogenous naphthaleneacetic acid cause bud release and development of rhizomes from previously inhibited axillary buds of the shoot. However, it was not possible to convert a shoot apex into a rhizome apex by auxin treatment. It is suggested that the release of buds on the lower side of horizontal branches and of buds directly above a stem girdle is caused by high auxin levels on the lower side or distal to the girdle. The experimental results are discussed in relation to naturally occurring shoot‐rhizome dimorphism.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10178.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

During early stages in the transition from 1‐ to 2‐dimensional gametophyte development the change from filamentous to bulbous apical cell is not accompanied by major changes in the nature or number of cytoplasmic components of the cell. However, chloroplasts in apical cells of plants grown in red light are larger than those from cells of plants grown in blue light. In addition, the orientation of cytoplasmic microtubules is different in apical cells of plants from red and blue light. This change in orientation may be causally related to the change in apical cell form during 1‐ to 2‐dimensional growth.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10179.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

Using scanning electron microscopy, we determined the kinds and distribution of epidermal cell types inAvenainflorescence bracts (glume, lemma, and palea). Electron microprobe analysis of silica deposition in these epidermal cells showed that silica cells constitute one of the important deposition sites. Probe ratio data indicate that the silica deposited is 74 % pure. Significant amounts of silica also become deposited in the trichomes and lesser amounts in the walls of long epidermal cells. None could be detected in the stomata. The possible functional significance of silica deposition in epidermal cells of these bracts is discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10180.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

The American Maydinae generaZeaandTripsacumcross readily when not isolated from each other by gametophytic barriers, and it has been suggested that intergeneric introgression played a role in the evolution of maize. FourZeachromosomes pair with members of at least one basic genome of tetraploidTripsacum, and in hybrids involving octaploidTripsacumall 10 chromosomes of the basic maize genome frequently compete successfully in synapsis withTripsacumchromosomes. Hybrids that combine 36Tripsacumand 10 maize chromosomes are female fertile. When they are pollinated by maize their offspring have 36Tripsacumand 20 maize chromosomes, or again have 36Tripsacumand 10 maize chromosomes, but the 10Zeachromosomes are contributed by the new pollen parent. Later backcross generations also include plants with 36Tripsacumand 12, 14, 16, or 18 maize chromosomes. Individuals with 2n = 56 produce an abundance of offspring with 18Tripsacumand 20 maize chromosomes when backcrossed with maize. Further backcrossing results in elimination ofTripsacumchromosomes, and eventually plants with 2n = 20Tripsacum‐contaminated maize chromosomes are obtained. Two generations of selfing restore full fertility to these 2n = 20 plants and eliminate all obvious traces ofTripsacummorphology.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10181.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

The quantitative composition of major sugars in the nectars of 35 plant species was compared with that of 12 fruit juices. The use of specific quantitative assays for glucose, fructose, and sucrose made it possible to analyze large samples without quantitative chromatographic separations. Sucrose ranged from 0–99%. In most nectars, glucose and fructose were present in approximately equal amounts. No evidence was found for the presence of maltose, raffinose, and other oligosaccharides.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10182.x

出版商:Wiley    

年代:1972

数据来源: WILEY

摘要:

Three plots representing two stages of old‐field succession and the climax were selected in each of three vegetation types in Oklahoma: oak‐pine forest, post oak‐blackjack oak forest, and tall grass prairie. Soil samples from the 0–15 and 45–60 cm levels were analyzed every other month for 1 yr for exchangeable ammonium nitrogen and for nitrate. On alternate months numbers ofNitrosomonasandNitrobacterwere determined in the 0–15 cm level. The amount of ammonium nitrogen was lowest in the first successional stage, intermediate in the second successional stage, and highest in the climax stand. This trend was remarkably consistent throughout all sampling periods, all vegetation types, and both sampling levels in the soil. The amount of nitrate was highest in the first successional stage, intermediate in the second successional stage, and lowest in the climax stand in both sampling levels, all vegetation types, and virtually all sampling periods. The numbers of nitrifiers were high in the first successional stage, generally, and decreased to a very low level in the climax. In fact, there was often noNitrobacterin the climax stands. These results indicate that the nitrifiers are inhibited in the climax so that ammonium nitrogen is not oxidized to nitrate as readily in the climax as in the successional stages. Evidence from other geographic areas and vegetation types strongly supports this conclusion. This would certainly appear to be a logical trend in the evolution of ecosystems because of the increased conservation of nitrogen and energy. The ammonium ion is positively charged and is adsorbed on the negatively charged colloidal micelles, thus preventing leaching below the depth of rooting. On the other hand, nitrate ions are negatively charged, are repelled by the colloidal micelles in the soil, and thus readily leach below the depth of rooting or are washed away in surface drainage. There is growing evidence also that many plant species can use ammonium nitrogen as effectively or more so than nitrate nitrogen. If ammonium nitrogen is used directly, this eliminates four chemical steps because nitrogen which is oxidized to nitrite and then to nitrate must be reduced back to nitrite and then to ammonium nitrogen before it can react with keto‐acids in the formation of amino acids. The two reduction reactions require considerable expenditure of energy.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1972.tb10183.x

出版商:Wiley    

年代:1972

数据来源: WILEY