Vincetoxicum indicum (Burm.f.) Mabb. - a case of transient abnormal secondary thickening in stem

Vincetoxicum indicum (Burm.f.) Mabb. (Syn. Tylophora indica (Burm.f.) Merr., T. asthmatica W. &A.), an important twining medicinal plant of India, was found to show a transient anomalous secondary thickening to facilitate the twisting of stem around a support. The very young stem had a continuous primary xylem cylinder, the protoxylem of which differentiated to two large bundles on the opposing sides and many smaller bundles in between. In the initial stages of maturation, the cambium outside the two large protoxylem groups behaved abnormally in producing more phloem outwards and little or no secondary xylem inwards to produce two wedge shaped phloem groups on opposite sides. The production of crescent shaped secondary xylem on the other two sides which fell at a right-angled plane resulted in bulging of these sides away from the anomalous cambium to create a rectangular stem having two broad sides which were used as the facing sides of stem against a support. As soon as the twisting nature was established, the anomaly was reversed and the anomalous cambial patches started behaving normally to produce a complete ring of secondary xylem. As this abnormal behaviour happened only during the twisting of stem, this is considered as an adaptational anomalous secondary thickening.

On self-injectivity of the f-ring Frm(𝓟(ℝ), L)

Let 𝓕𝓟L := Frm(𝓟(ℝ), L). We show that if L is a P-frame then 𝓕𝓟L is an ℵ0-self-injective ring. We prove that a zero-dimensional frame L is extremally disconnected if and only if 𝓕𝓟L is a self-injective ring. Finally, it is shown that 𝓕𝓟L is a Baer ring if and only if 𝓕𝓟L is a continuous ring if and only if 𝓕𝓟L is a complete ring if and only if 𝓕𝓟L is a CS-ring.

Stem anatomy and development of interxylary phloem in Strychnos bredemeyeri (Loganiaceae)

En Strychnos bredemeyeri, pequeñas porciones de cambium dejan temporalmente de producir xilema secundario y produce más floema centrífugamente. Un nuevo segmento del cambium se diferencia en la parte exterior de este floema formado, entonces estos se unen al cilindro regular para formar un anillo. Esta repetida actividad da como resultado la inclusión de islas de floema dentro del xilema secundario, llamado floema interxilar. Luego aparecen nuevos elementos del floema asociado al cambium y a las islas de floema que aplastan los elementos no conductores de islas de floema. Junto al floema interxilar, el floema intraxilar está formado por la adición desde las células marginales de la médula. Posteriormente, pequeños arcos del cambium interno se inician en el borde interno del protoxilema en tallos gruesos. In Strychnos bredemeyeri small segments of the cambium cease to produce secondary xylem temporarily and produce more phloem centrifugally. A new segment of the cambium differentiates outside to this phloem, which unite with the regular cylinder to form a complete ring by leaving the cambium segment in the furrow. Such repeated activity of cambium results in inclusion of phloem islands within the secondary xylem, called interxylary phloem. New phloem elements added by the cambium associated with phloem islands crush the non-conducting sieve elements in older phloem islands. Beside interxylary phloem, intraxylary phloem is added from the marginal pith cells. Subsequently, small arcs of the internal cambium initiate on the inner margin of the protoxylem in thick stems.