An experimental and cytological study of the life history of Endophyllum Sempervivi

Abstract

The sporidia of Endophyllum Sempervivi are precociously binucleate. Entrance to the host cell is gained by penetration of the epidermal wall by a fine hypha. The infection vesicle is at first a spherical binucleate sac. Elongation of the part most remote from the point of entry occurs, and subsequent septation takes place. Further growth results in the production of a mycelium of uninucleate cells which is inter- and intra-cellular and passes down to the base of the leaf where it enters the stem. No hypertrophy of the leaves occurs at this stage. Perennating mycelium spreads through all the tissues of the stem except the vascular tissue and the apical meristem, and there passes the winter. On renewal of activity in the spring, the mycelium passes to the leaves and causes hypertrophy by elongation. It becomes massed in the subepidermal tissues, especially in the substomatal spaces. Emergent hyphae are frequently seen protruding through the stomata. Spermogonia are the first organs to be developed and occur markedly below stomata. These are accompanied by wefts of aecidial primordia composed of uninucleate cells. Later a secondary growth appears at the base and the hyphae become binucleate. The diplophase may be initiated by nuclear migration. The nuclei of each binucleate cell divide conjugately and from the aecidiospore mother cell formed an aecidiospore and intercalary cell are produced. The spores may be quadnnucleate whilst still enclosed in the peridium. They germinate to give rise to a three-septate promycelium and abstrict four sporidia. Experiments made to determine the function of the spermatia show that the mature aecidia can be formed when the sper-matia are (a) removed by burning out with a hot needle, or (b) kept in position by the application of a smear, e.g. vaseline, liquid paraffin, “Fixatif” or a solution of mercuric chloride.