1906] SMITH—A NEW FUNGUS 221 
Pythiacystis Smith & Smith, n. gen. 
Parasitic on living plants, or saprophytic with abundant moisture. 
Fertile mycelium delicate, septate, with numerous, terminal, sym- 
podially developed sporangia. Aquatic mycelium typically sterile, 
with occasional conidia or sporangia. Filaments very large and 
vigorous, continuous, much branched. 
Sporangia typically rounded or ovate, dividing internally into 
biciliate swarmspores which immediately become motile and emerge 
from a terminal opening, 
Conidia similar to sporangia, germinating directly by a germ 
tube. 
Sexual reproduction not observed. 
Differs from Pythium in mode of swarmspore formation, and from Pythiopsis 
in habit. Closely intermediate between Saprolegnieae and Peronosporeae. 
Pythiacystis citrophthora Smith & Sm’ 4, n. sp.—Parasitic on 
lemons, and occasionally other Citrus fruits, .ausing decay of green 
fruit on the tree and in the storehouse. Mycelium in affected 
fruit sterile, inhabiting rind and fibrous portions. Internal, except 
in moist air, Mycelium in water or nutrient liquids very vigorous, 
usually sterile, or occasionally with conidia or sporangia. Fruiting 
Stage found typically in moist soil, in contact with affected fruit. 
Sporangia ovate or lemon-shaped, sometimes rounded, considerably 
elongated, or double, with terminal protuberance; 20X30 to 60 
X90H, AV. 35X50 4. Produced in great abundance under favorable 
conditions, In water dividing quickly by internal division into 
5 to 40 (usually about 30) swarmspores, which are immediately 
set free and discharged through a terminal pore. 
Swarmspores 10 to 16 w in diameter, at first elongated, becoming 
rounded ; with two lateral cilia 30 to 40m in length, Actively 
motile when discharged, soon coming to rest and germinating. 
Fungus abundant in winter and spring in southern California lemon orchards 
and packing houses, causing serious losses. 
UNtverstry oF CALIFORNIA, BERKELEY. 
