Apr. 21, X923 
Gummosis of Citrus 
211 
neath frequently develop a disagreeable fetid odor.® The bark dies and 
breaks away in patches, leaving bare, dead areas, which spread in all 
directions, but raostly downward, on the main crown roots and laterally 
around the trunk. Trees thus affected bear heavy crops of fruit and the 
leaves become yellow. 
Phytophthora terrestria Sherbakoff (55) was first isolated by the writer 
from gumming lesions of an orange tree at Lindsay, Calif., in 1912, and 
was considered at that time to be only a peculiar strain of Pythiacystis 
citrophthora. Later, in 1914, it was isolated from mal di gomma lesions, 
as follows: (i) from a grapefruit tree at Palmetto, Fla. (2d, fig^ 5); (2) 
from orange trees in Cuba; and (3) from a tangelo tree on the Isle of Pines. 
The Florida and Cuban cultures were still considered to be strains of 
Pythiacystis dtrophthora and were referred to as such in publications (25, 
2d). Stevens (dr) later made an extended survey and isolated this 
species in a large number of mal di gomma cases from widely separated 
localities representing the principal part of the Florida Citrus belt. In 
the meantime, Sherbakoff (55) had described Phytophthora terrestria as 
causing rot of tomatoes in Korida. The cultures previously isolated at 
Lindsay, Calif., and in Florida and Cuba were then examined by Sher¬ 
bakoff, who concluded that they were all the same species. A culture 
isolated by George Fawcett from a lemon tree in Argentina and sent to 
the writer in October, 1916, was also determined to be similar to this 
species. Later, the writer (27) determined that Phytophthora terrestria 
had markedly different growth-temperature relations from those of 
Pythiacystis dtrophthora. The vegetative growth on certain culture 
media, the method of forming sporangia, and the effect on the host 
when inoculated, are so similar, however, as to make it seem probable 
that the two are closely related species. (See inoculation experiments, 
Tables XI and XII.) 
Phytophthora terrestria is believed by some authors to be identical 
with P. parasitica Dastur. Ashby (4) has recently described a leaf¬ 
stalk rot of coconuts in Jamaica as being due to this latter fungus and 
states that Dastur has compared P, terrestria with P. parasitica and 
found them to be identical. Ashby has also found this fungus on tobacco 
and pineapple plants. Dastur (19) originally described his species as 
causing a disease of castor oil plants in India and later (20) found it 
attacking Vinca rosea. If P. parasitica and P. terrestria are the same 
species, a wide distribution of this fungus is indicated. * 
Comparative Inoculations with Phytophthora Terrestria and Pythiacystis 
Many different series of inoculation experiments with Pythiacystis 
dtrophthora and Phytophthora terrestria were made under varying con¬ 
ditions, the results of some of which are given in Tables XI and XII. 
® This rotting of the wood, as well as the bark, and the accompanying "fetid odor" are believed to be due 
mainly to secondary organisms setting up fermentation and decay below the surface of the soil after killing 
of the bark by the primary organism. While gum may be formed below as well as above the surface of 
the soil, it is dissolve readily by moisture and is usually less conspicuous below the soil surface. 
