Developmental Studies of Two Species of Nowakowskiella Schroeter: N. ramosa Butler and N. profusa Karling

Abstract

N. ramosa and N. pro-fusa were examined from a physiological and a developmental point of view. Both spp. grow well on a solid substrate of cellulose-like composition, as contained in the pericarps of cereal grains and hemp achenes and cellophane, if the surrounding liquid contains organic decomposition products. N. ramosa has an opt. temp. of 16-18 C and N. profusa of 24-28 C; but both spp. can be adapted to other temps. The cell walls of both spp. are predominantly chitin intermixed with cellulose. A 2d inner wall-layer is present in N. ramosa but not in N. profusa. The opercula in the zoosporangia of both are pectinaceous. The behavior of the protoplasm in development is similar to that in other chytrids. Food material exists as a mixture of granules and lipoids which separates into the nuclear cap and oil globule in the zoospore. The flagellum of the zoospore is a complete organelle with a blepharoplast connected to the nucleus by a rhizoplast. The center of growth is early transferred from the spore-case to a swelling in the single unbranched germ-tube. Intramatrical trophic thallus of swellings, isthmuses, and rhi-zoids resembles the complete thallus of the more typical poly-centric chytrids. The trophic "mycelium" is functional in the mature thallus and gives rise to distinct extramatrical reproductive branches which bear intercalary and terminal zoosporangia. The term "rhizomycelium" is not believed adequate to characterize the differentiated thallus structure.