摘要:

In freshly matured seeds of the long‐lived monocarpic perennial,Frasera caroliniensisWalt., the embryos are underdeveloped and physiologically dormant. Dormancy was broken by a long period of stratification (chilling) at 5 C. Seventy six percent of the seeds germinated at 20 C (day)/10 C (night) after 98 days of chilling at 5 C, while seeds kept at 5 C germinated to 87% after 205 days. A warm, moist pretreatment was not required for subsequent breaking of dormancy at 5 C. Embryos in fresh seeds averaged 1.3 mm long, but after 12 weeks of chilling they averaged 4.1 mm. Thus, the embryos require a period of chilling to become fully developed, after which seeds can germinate at the afterripening temperatures (5 C) or at some higher temperature. Seeds ofF. caroliniensisfit Nikolaeva's (1977) morpho‐physiological complex dormancy type.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06358.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

The effect of pH 5–8 and lichen acid concentration gradients (2.7 times 10−2‐ 2.7 times 10−6m) on the toxicity of the following lichen acids: usnic, lecanoric, evernic, vulpinic, stictic, fumarpro‐tocetraric, psoromic, and atranorin, on spores ofFunaria hygrometricawas tested. Percent germination and sporeling growth were used as indicators of toxicity. None of the lichen acids were significantly toxic, for either percent germination or sporeling growth at concentrations equal to or below 2.7 times 10−5mat pH 7.0, but many of the lichen acids which increased in toxicity at values different from pH 7 may have been toxic at lower concentrations if a different pH was used for the assay. Lichen acid toxicity showed a good correlation with pH for the parameter of spore germination, or sporeling growth, or both. Some lichen acids did not inhibit germination but were effective in retarding sporeling growth, or vice versa. This observation is discussed in relation to changing fatty acids and other lipid composition as germination occurs. Two of the threeO‐methylated lichen acids (evernic and psoromic) were among the most effective in inhibiting growth over all, but at lower pH values these were less effective than non‐O‐methylated lichen acids. Stictic, which is also anO‐methylated lichen acid, was the least effective inhibitor over all the pH values for both parameters, while vulpinic was the most toxic over all the pH values. The order of relative toxicity for the lichen acids is different, depending on the pH and concentration at which they are tested and depending on the parameter measured. Thus, in an ecological sense, it is difficult to evaluate the adaptive significance of a particular compound or group of compounds without knowing what factors influence the toxicity of those compounds and how these factors vary in the organism's habitat.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06359.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

The shoot apical meristems of adultEchinocereus engelmanniiplants are zonate and have a tunica, central mother cells, a peripheral zone, and a pith‐rib meristem. An ultrastructural, stereological study showed that each zone has its own distinct ultrastructure, but that the differences between the zones are quite small, both on a protoplasmic basis and on a cytoplasmic basis. Furthermore, the ultrastructure present in the adult apices differed only slightly from that which had been found in seedling apices, demonstrating a long‐term stability of structure. The standard deviations found in the sample were small, indicating little variability from one plant to the next and suggesting that there are little or no cyclic changes during the plastochron or a 24‐hr photoperiod. The ultrastructures found in the shoot apical meristems differed significantly and markedly from mature tissues of the same plants.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06360.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

Various morphometric parameters of shoot apical meristems were measured during the ontogeny ofMelocactus matanzanusandTrichocereus pachanoi. While some ontogenic features varied dramatically (i.e., apical surface curvature, dK/dl, varied by 0.15–0.17, while the apical volume increased from 105μm3to 107or 108μm3), the percent volume of the central‐mother‐cell zone (CMCZ), pith‐rib meristem (PRM), and the peripheral zone (PZ) showed remarkable intraspecific constancy: CMCZ = 9.2%, PRM = 10.4%, PZ = 80% forM. matanzanus, and CMCZ = 10%, PRM = 24.5%, PZ = 65% forT. pachanoi. Seedlings (2 plastochrons old) showed distinctly different percent volumes from older forms: CMCZ = 7.8%, PRM = 5.9%, PZ = 86% forM. matanzanus, and CMCZ = 8.9%, PRM = 13%, PZ = 77% forT. pachanoi. Geometric expressions of cell patterns within zones of the apex remained relatively constant throughout development. On the basis of intra‐ and interspecific comparisons of the percent volumes among 23 taxa and the chronology in the appearance of zones within the apex, it is concluded that while there are no apparent biological reasons for the actual percent volume values computed from our sample set, the constancy in zones reflects a high degree of homeostasis which is achieved early in ontogeny.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06361.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

Anthochlors (chalcones and aurones) are found in a number of plant families including the Compositae. Within this family they were once thought to occur only in the subtribe Coreopsidinae of the tribe Heliantheae. More recent studies show them to occur also in the tribes Cardueae, Eupatorieae, Helineae, Inuleae, and Lactuceae. This has suggested that anthochlors are no longer good taxonomic markers for the Coreopsidinae. A survey of 69 of approximately 210 genera of the Heliantheae shows anthochlors present only in the Coreopsidinae except forHelianthus, Simsia, Tithonia, andViguiera, closely related genera of the subtribe Helianthinae. Of the 32 genera of the Coreopsidinae recently recognized, 30 were surveyed from available material and all contain anthochlors exceptGuardiolaandVenegasia. The results indicate that, despite some variation, anthochlors are still good taxonomic markers for the Coreopsidinae. This represents the only case within the family in which a particular type of flavonoid is taxonomically diagnostic at the subtribal level.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06362.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

Morphological and anatomical changes in shoots of vigorously growing cottonwood plants (Populus deltoidesBartr.) were studied during dormancy induction in 8‐hr short days (SD) and in control plants grown in 18‐hr long days (LD). Pronounced structural changes occurred in terminal buds after 4 wk and full dormancy was achieved in 7 wk of SD. Leaf expansion ceased after 5 wk of SD as foliage leaves matured to the terminal bud base at leaf plastochron index 0 (LPI 0). Within the bud, total leaf length (lamina + petiole) decreased and stipule length increased progressively each week; thus, the ratio total leaf length/stipule length decreased rapidly, especially at the position of incipient bud‐scale leaves LPI ‐ 1 and LPI ‐ 2. These bud‐scale leaves were fully developed by wk 6 and were derived from enlarged stipules and aborted laminae. The full complement of primordia within the bud at the start of SD eventually matured as foliage leaves and the first bud‐scale leaf (LPI ‐ 1) was initiated immediately following transfer to SD. Acropetal advance of the primary‐secondary vascular transition zone (TZ) was associated with leaf maturation. However, it did not advance throughout the entire vascular cylinder as in LD, but only in those leaf traces serving mature leaves beneath the terminal bud. In both LD and SD treatments the same linear relationship was maintained between LPI of the TZ and LPI of the most recently matured leaf; both parameters simultaneously increased in LD and decreased in SD. Thus, the relationship between leaf maturation and advance of the TZ was maintained irrespective of environment.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06363.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

Crystal forms and crystal structure of the metastable polyhydrate (weddellite) and the stable monohydrate (whewellite) occurring in plant cells are described and their formation as well as their physiological bearing are discussed.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06364.x

出版商:Wiley    

年代:1981

数据来源: WILEY

摘要:

Vascular pattern and anomalous secondary growth were studied in shoots ofClytostoma callistegoides, a liana having two types of phyllotaxy, one decussate and the other whorled. In shoots with decussate phyllotaxy, typical of bignoniaceous lianas, the vascular pattern has four major vascular strands that extend continuously from internode to internode, whereas in shoots having a whorled phyllotaxy the pattern has six major vascular strands. The first unidirectional cambium segments which result in the anomalous secondary growth were initiated precisely opposite each of the major vascular strands in both types of shoots. It is concluded that positioning of unidirectional cambium segments responsible for anomalous growth is correlated morphogenetically with the vascular pattern.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06365.x

出版商:Wiley    

年代:1981

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06366.x

出版商:Wiley    

年代:1981

数据来源: WILEY

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1981.tb06346.x

出版商:Wiley    

年代:1981

数据来源: WILEY