THE MATERIAL OUTGO OF PLANTS 
333 
tissue and to deserve the name water gland; in others it seems to be 
passive. 
Guttation in fungi. Guttation is not confined to the higher plants, 
nor are there always such elaborate accessory structures. It occurs in 
its simplest form in many fungi. Thus Pilobolus crystallinus owes its 
specific name to the droplets of water which appear on its sporangio- 
phores (fig. 630), and Mendius lacrymans, the dry-rot 
fungus, likewise, " weeps " so much water that it accum- 
ulates in big drops on the surface of its sheetlike 
mycelium. 
Nightly guttation. In nature the checking of evapo- 
ration, which results in guttation, occurs chiefly at night, 
when many young plants exude water. What remains 
adherent at the water pore may be partly resorbed when 
transpiration begins. 
This seems to be the way in which a destructive bacterial dis- 
ease of cabbage infects the plants. By contamination of the 
hanging drop the bacteria find their way into the chamber as the 
drop evaporates or is resorbed, there develop and -so kill the 
adjacent cells, whence they enter the xylem bundles and work 
backward, killing and rotting the bundles. When the crop is 
gathered and stored, they develop further, until the head is spoiled 
by the extension of the blackened and rotted tracts in the blanched 
leaves. 
FIG. 630. 
Sporangiophore 
of Pilobolus, 
showing ex- 
uded water. 
Adapted from 
ZOPF. 
One may easily observe the exudation of water from the leaves of 
lawn grasses early in the evening, when the " dew " is said to be " fall- 
ing." The warm soil conduces to the entry of water; the cooler air 
checks evaporation ; these conditions permit maximum turgor ; gutta- 
tion at the tips of uninjured leaves, or, more often and more promptly, 
bleeding from the cut ends of the leaves is the result. Dew, of course, 
may form under proper conditions; but exuded water forms a great part 
of what passes as dew. 
Artificial guttation. Guttation may be produced artificially by injecting water 
under pressure into the stem of a plant known to have water pores, as by attaching 
the end of a cut shoot to a water tap. Presently droplets exude at the usual places. 
It is usually assumed that the water is thereby forced through the plant tissues, 
but as city water pressure varies from 2-3 atmospheres (seldom more, and less 
will often answer), it is doubtful if so low a pressure (as compared with the 310 
atmospheres of common turgor pressure) would be adequate to do this (see further, 
P-33 6 >- 
