On the Reproduction of some Marine Diatoms

Abstract

The subject of the production within Diatoms of spores, en docysts, &c., has been worked at by several observers, principally Castracane in recent years, and before him O'Meara and Rabenhorst. Some of these observers have noted ciliated, spore-like bodies, probably parasitic or casual intrusive organisms; others, notably Castracane, have recorded oval and other cysts winch have not been figured and the characters of which are difficult to realise. Miquel has made an experimental examination of the subject without being able to confirm Castracane's results. Castracane has also recorded the presence, as he thinks, of “gonids or embryonal forms” within a fossil Diatom (Coscinodiscus punctatus) in a marine deposit of miocene age. During March of this year I tow-netted near the Bell Rock a large quantity of Coscinodiscus concinnus — with many dead valves separated at the girdle. These frequently contained not only other and smaller individuals of the same species, but other species of diatoms and casual objects as well, and the observation makes one cautious about accepting evidence of the character brought forward by Castracane as to his fossil form.Lauder, in describing forms of Bacteriastrum and Chœtoceros, observed the formation of endocysts. “At certain times, or under certain circumstances, the endochrome does not divide after the lengthening of the frustule, but secretes a siliceous envelope and becomes a gonidium or sporangium, consisting of a cell with two rounded ends, and a connecting hoop, one end being smaller than the other ….