BRIEFER ARTICLES 
A PARASITIC ALGA, RHODOCHYTRIUM SPILANTHIDIS 
LAGERHEIM, IN NORTH AMERICA 
During February, 1908, Dr. F. L. Stevens, of the North Carolina 
Agricultural College, sent me a few dried leaves of the common ragweed, 
Ambrosia artemisiaefolia, which contained a very interesting parasite. 
Externally it suggested the appearance of a Synchytrium, because of the 
humerous minute red dots distributed beneath the surface on the petioles 
and veins of the leaf and on the stem, although there was no gall forma- 
tion similar to that caused by species of the Synchytriaceae. A section of 
the host, however, showed clearly that it was very different from any of 
the members of this family. Maceration or teasing of the host tissue 
revealed the presence of a mycelium, and the crowded condition of the 
fruit bodies suggested the genus Cladochytrium. Further study proved, 
however, that it was a unique type, very different from members of this 
genus. Since the material received was dead, it was impossible to obtain 
the zoospores, and Dr. STEVENS kindly promised to have fresh material 
sent me at stated times during the summer. 
Beginning in the month of June, material was collected by Mr. J. G. 
HALL, assistant in botany at the North Carolina Agricultural College, and 
mailed once a week. Entire plants were collected, the roots were washed, 
and then packed mostly in pasteboard boxes with wet sphagnum. In this 
way they reached me in two or three days after shipment in very good condi- 
hon, so that some of the parasitized ragweed plants were transplanted in 
the open and others in pots where they continued to grow. 
From a study of this material I have been able to obtain the zoospores 
from the temporary zoosporangia and to work out certain stages in the 
life-history of the parasite. While searching the literature for unique 
forms of plant parasites, I discovered that this plant had been described 
fen years ago. 
This remarkable parasite is Rhodochytrium spilanthidis Lagerheim.* 
It was first discovered by LAGERHEIM in 1889 near Quito, Ecuador, and 
later Was observed by him in other provinces of Ecuador. In Ecuador it 
‘S Parasitic on the stems and leaves of a species of Spilanthes, one of the 
; LAcERHEM, G. DE, Rhodochytri nov. gen., eine Uebergangsform von den 
Protococcaceen zu den Chcuideeen: ak its 51:43-53- pl. 2. 1893. 
299] [Botanical Gazette, vol. 46 
