Ghytridium alarium on Alaria fistulosa 



Alice L. Kibbe, 

 University of Washington, Seattle. 



While preparing slides for a paper on Alaria fistulosa, certain struc- 

 tures not to be accounted for as necessary parts of the alga were ob- 

 served. They appeared in various forms in all parts of the plant except 

 the heavy, older portion of the stipe. At that time a consideration of 

 them was deferred until the paper in hand was completed. It seemed 

 certain, however, that the bodies represented a fungus parasitic on Alaria 

 fistulosa. This paper traces the life history of this fungus, Chytridium, so 

 far as it could be determined from preserved material. Fresh material, 

 and well killed material, were greatly needed ; but the opportunities for 

 getting them seemed too distant to withhold publication longer. 



Examination of all of the species of brown algae readily available at 

 the Marine Station at Friday Harbor showed no trace of this fungus 

 m any of them. Alaria valida, from Alaskan waters, was also examined, 

 but it was not infected. It was found in every specimen of A. fistulosa 

 examined. The fungus is least abundant in the stipe, appearing only at 

 its upper end, and scantily there. It groAvs scantily in the angle where 

 the thin part of the blade joins the midrib. It is more abundant in the 

 older portions of the midrib than in the growing region. It is abundant 

 in the thin portion of the blade but does not commonly maintain its nor- 

 mal shape there, being more nearly globular, or even flattened parallel to 

 the surface. In the sporophylls it attains its best development. Prob- 

 ably this is due to the i3ellicle above the sporangia of the host tending 

 to protect the fungal sporangium. The sporangia and paraphyses are 

 readily pushed aside by the fungus, and give space in which the sporangium 

 of the parasite may expand. The parasite readily pushes its way through 

 the pellicle when the spores are about to be discharged. The spores prob- 

 ably become motile before they enter the host plant. 



The materials sectioned were collected by Dr. T. C. Frye and Dr. 

 G. B. Rigg, on the United States Bureau of Soils Kelp Investigation Ex- 

 peditions to Alaska in 1913. It was killed and preserved in two percent 

 formaldehyde. The best stain was erythrosin, but safranin proved fairly 

 successful. Good material for drawings was secured by allowing slides 

 to stand for some time in alcoliol which had been used to draw safranin 

 stain. In this way the host was lightly stained, while the fungus retained 

 its characteristic yellowish to brownish color. Heavy stains are wliolly 



(221) 



