142 Scientific Proceedings, Royal Dublin Society. 



readily iu water, and form the usual uniciliate zoospores, which in wet soil 

 infect neighbouring roots, probably through the root-hairs. Marchal found, 

 e.g., that the zoospores spread the disease a distance of 20 cms. (8 inches) in 

 all directions in 24 hours. 



Eesting sporangia are common in older plants, and have been shown to 

 be the means of propagating the disease from season to season, though their 

 actual germination has not yet been observed. 



Flax-yellowing is a disease of youth. The critical period of attack varies 

 between the thirteenth and twenty-fifth day after the time of sowing, and is 

 partly dependent on the weather, especially the temperature. Asterocystis 

 occurs also on the roots of grasses, and of many weeds found in a flax-field. 

 Its eradication depends mainly on crop-rotation (in which flax comes once in 

 seven or even ten years), hel])ed by the pulling up and burning of the 

 diseased plants. Flax soil, says Marchal, should not receive excess of 

 nitrogenous manure, but a sufficiency of phosphoric acid. The extensive 

 manurial experiments carried out by the Irish Department of Agriculture 

 each year since 1901 demonstrate " that as regards artificial manures potash 

 should be the dominant, if not the sole, manurial ingredient in those used 

 for flax." Muriate of potash, at the rate of \-\\ cwt. per statute acre, mixed 

 with sand, fine soil, or sawdust, is recommended for application (17). The 

 Department finds that this potash manure prevents flax-yellowing in Ireland, 

 and, as a result, for the last two or three years very few cases have come in 

 to me for report. Marchal, however, found the zoospores of Asterocystis 

 bore easily a dose of 0'02 per cent. (1 in 5,000 parts) of potash iu their food 

 solutions or in soil. 



Marine Chytuidiace^. 



I have collected from various parts of the coast of Ireland algse infested 

 with Ohytridians. One of these, on a species of Ectocarpus, was described 

 by Dr. B. P. Wright (18) as Rhizophidium Dkksonii. In his monograpli 

 of tlie group, A. Fischer says of this species the sporangia are of very 

 abnormal form ; and the relation of the parasite to its host seems to deserve 

 fresh investigation, as its sporangium appears, from the figures, to lie partly 

 within the host-cell. Bhizophidium Schenk shows an external sporangium 

 and an internal rhizoidal or haustorial mycelium. My intention to act 

 on Fischer's suggestion by an examination of the collected material was 

 anticipated by P. Magnus, who gives the results of his examination in 

 Hedwigia in 1904, N. Wille having already in 1899 decided that the plant 

 was not a Eliizophidium, as it possesses no signs of a mycelium. He called 

 it Olpidium Dicksonii. Magnus, it seems, had the plant before him in 1875 

 (two years before Wright's account appeared), when describing the Marine 

 Olpidese, but left it unnoticed for the time being. He now regards it as 



