118 
PACIFIC SCIENCE, Vol. Ill, April, 1949 
The pineapple plant is slow to respond to root 
injuries and, under Hawaiian conditions at 
least, populations of other nematodes may be 
markedly reduced by biological agents after they 
have inflicted root damage but before top 
growth shows the effect. Lack of correlation 
between abundance of paratylenchs and plant 
condition is therefore not proof of harmless- 
ness. It seems improbable that such popula- 
tions as are encountered around pineapple roots 
could obtain their entire sustenance from the 
roots without in some way altering absorptive 
action or speeding senescence if not even alter- 
ing the physiology of the entire plant. 
Regardless of any minor or delayed patholo- 
gical effects of its feeding, this paratylench ob- 
tains its food without immediately endangering 
its food supply. It may therefore be considered 
a well-adjusted parasite. The precise way in 
which it obtains its food from cells that char- 
acteristically are highly vacuolated remains un- 
determined. By analogy with the predaceous 
Aphelenchoides and the gall-inciting Hetero- 
dera marioni (Linford, 1937 a\ 42-44; 1937£; 
1942;*) the periods of rest of the esophageal 
bulb, alternating with periods of rapid pulsa- 
tion, are presumably periods of injection into 
the host of glandular secretions that selectively 
prepare nutrients for ingestion. Saliva of pre- 
daceous aphelenchs, however, is vigorously di- 
gestive, and that of the root-knot nematode 
stimulates profound changes in the protoplasts 
of cells into which it is injected in addition to 
any function it may perform in reducing some 
of the protoplasm to a state suitable for passage 
through the narrow lumen of the stylet. In both 
of those types of nematode the quantity of 
saliva is relatively copious, and it must dis- 
tribute freely to perform its functions. In the 
paratylenchs, however, with small esophageal 
glands, one would expect the saliva to be limited 
in quantity or to be secreted only slowly. It is 
not remarkable, therefore, in view of the minute 
size of these nematodes and of the limitations 
placed upon microscopic study by illumination 
only with incident light, that no flow of saliva 
has been detected. Neither could ingestion of 
food be seen under these conditions even 
though it obviously occurred during pulsation 
of the bulb. Unfortunately it was not possible 
to determine whether the granular accumula- 
tion around the tip of the stylet consists only 
of host cytoplasm or, in part, of secretions from 
the nematode. That it is not wholly normal 
cytoplasm was indicated by the temporary per- 
sistence of at least part of the mass for a time 
after the stylet had been withdrawn. If a small 
quantity of saliva is injected it could probably 
function to the greatest advantage and with 
the least disturbance of the host if it remained 
localized close to the stylet, acting upon cyto- 
plasm clumped about the stylet, rather than 
distributing throughout the proportionately 
large host cell. Indicative of extra-oral diges- 
tion is the lack of a functional anus and of dis- 
cernible fecal material in the rectal region. 
This is in sharp contrast to various other nema- 
todes of somewhat comparable size but different 
food habits in which discharges of fecal ma- 
terial are readily detected. Even with selective 
ingestion of almost wholly utilizable nutrients, 
however, there should be a great excess of 
water to be excreted. Perhaps this is discharged 
unnoticed through the excretory pore, carry- 
ing with it all soluble waste materials. 
There seems no doubt that P aratylenchns 
minutus is an obligate parasite, obtaining all 
of its nutriment from living cells, yet this fact 
is not readily determinable by any means other 
than direct observation of the living nematodes 
in association with roots. Greater abundance of 
nematodes near roots than in. soil remote from 
them is not a valid criterion of parasitism, be- 
cause various microphagous and predaceous 
nematodes similarly congregate in the rhizo- 
sphere where their food is most abundant. 
Dead rootlets, killed by fungi or other agents, 
soon are invaded by non-parasitic forms. Simi- 
larly, occurrence of moderate numbers of a 
species within relatively sound roots is not evi- 
dence of parasitism since microphagous forms, 
working over the root surface, may enter 
