Spore discharge in Cordana musae (Zimm.) H?hnel and Zygosporium oscheoides Mont.

In Cordana musae and Zygosporium oscheovides violent spore dischargeoccurs under conditions of rapidly decreasing vapour-pressure;discharge is not dependent on light. Mechanisms of dischargeare postulated. In C. musae, on drying, water evaporates frominside the conidium and conidiophore, causing a negative pressureto develop in the solutions inside these structures and thewalls to be drawn inwards under tension. The sudden appearanceof a gas bubble in one or both of these structures releasesthe tension, and the resultant jolt causes the conidium to beshot away. In Z. oscheoides similar tension and wall distortiondevelop in a specialized conidiophore cell, the vesicle, onwhich the conidia are poised. On appearance of a gas phase,the vesicle wall springs back to its original form and the conidiaare shot away. The vesicle is likened to a single annulus cellin the fern sporangium. The similarity between discharge inC. musae, Z. oscheoides, and Deightoniella torulosa is brieflydiscussed.     

Quantitative Aspekte der regressiven Evolution – dargestellt am Beispiel der Augenrückbildung bei Höhlenfischen

Quantitative aspects of regressive evolution – demonstrated by the reduction of the eyes in cave fishes According to our present understanding, the eyes of cave fishes are no longer subject to a stabilizing selection. Because of a strong mutation pressure in the destructive direction, this leads to a continual enrichment of elimination mutants and thereby to a progressive reduction of the eyes after separation of a cave population. Obviously a natural selection process does not play a significant role in the reduction of the eyes in cave fishes. Based on these findings, the degeneration process can be characterized in detail, especially concerning its course and duration.     

Regressive und rekonstruktive Evolution bei Höhlenfischen -zwei Formen besonders schnellen phylogenetischen Wandels

Regressive and reconstructive evolution in cave fishes - two modes of especially rapid phylogenetic change If a characteristic loses its biological significance, it is no IonGer reulated by a stabilizing selection rocess. Its polygene system will be progressively inactivatecf by continual mutation, and the characteristic will degenerate by regressive evolution. However, if a system of modifying genes faces uncontrolled exposure to general mutation pressure and gradually loses its effectiveness, a derepression of fundamental genetic potencies can occur, bringing about the expansion of a trait that is already present, a reconstructive evolution. Both modes of evolution result in the extensive morphological and behavioral alterations of cave fishes before a reproductive separation from their surface-dwelling ancestral forms has occurred, making them distinct species.