F. H. Stewart 
177 
High humidity assists migration by approximating the conditions of life 
on the plant surface to those prevailing in the mesophyll spaces. It is not, 
however, essential to migration ( vide p. 175, and since Aphelenchus disease 
prevails in the open air). 
Sorauer (1902) maintains that Aphelenchi cannot invade healthy plants, that a disease of 
the vascular bundles is produced in pot plants grown at a temperature above the optimum, 
and that Aphelenchi enter such diseased plants only. Marcinowski (1908), on the other 
hand, infected healthy begonias in a natural manner. 
Aphelenchi are attracted by cell sap. I found that they collect in con¬ 
siderable numbers in plant wounds. Molz’s theory of entry through wounds 
is doubtless true in a limited sense; the injuries to which he refers are caused 
by insect parasites, and by the eruption of axillary buds. 
Certain races of many species of flowering plants are immune to the 
parasite (see lilt, passim and Molz, 1909). 
X. METHODS OF COMBATING THE DISEASE. 
Chemical treatment is of use only in such plants as Everlasting (Mangin, 
1895), if the blotching appears after the harvest, when the flowers are stored 
in warehouses. Exposure to a dry atmosphere saturated with carbon bi¬ 
sulphide for 24-48 hours, kills the parasites without affecting the appearance 
of the plants. In no other plants has chemical treatment of any kind been 
found of avail, since chemicals of sufficient strength damage the appearance 
of the plant. 
Treatment hy heat . Marcinowski (1910)—immersion of the plant in water 
at 50-52° C. for five minutes, kills the parasite but not the plant. 
Prophylaxis based on the habitat of the parasite in the surface of the soil. 
Earth for filling pots or boxes should be dug from a pit, surface earth being 
rejected. For open air culture deep ploughing of infected fields may prove 
useful. All infected leaves and plants should be burned. If it is necessary to 
use infected stock plants, they should be treated by the hot-water method, 
or by burying to a depth of at least three inches—after daily watering for at 
least a week, the surface earth should be removed, after which it is unlikely 
that any Aphelenchi will remain on the plant. 
XI. TECHNIQUE. 
Fixatives. Carnoy’s chloroform-acetic-alcohol mixture, Schaudinn’s or 
Bouin’s fluid, and boiling 70 per cent, alcohol are satisfactory; the first-named 
gives the most clear definition. 
Stains for mounting in toto haemalum differentiated with acid 70 per cent, 
alcohol, following Carnoy or Schaudinn is best; after Bouin, picrocarmine 
gives the best stain. 
Mounting. Looss’ alcohol-glycerine evaporation method, followed by 
glycerine jelly for unstained specimens. For stained specimens transfer to 
xylol, and add Canada balsam very gradually on several successive days. 
Farasitology xiii 
