PARASITES Or 
all, but in Germany a species common in grain fields } and 
the eyebright, which abounds in grass fields, are respectively 
known as “hunger” and “milk-thief,’ from the injury 
they do to the plants on which they fasten themselves. 
The mistletoe is a familiar example of a half-parasite, 
which roots on branches (Plate IX). Among the scanty 
belts of cottonwood trees along streams in New Mexico it 
is necessary to lop off the mistletoe every year to give the 
tree any chance to grow. Half-parasites may be known 
from plants that are fully parasitic by having green or 
greenish foliage, while complete parasites have no chloro- 
phyll and so are not at all green. 
406. Wholly Parasitic Seed-Plants.— These are so nearly 
destitute of the power of assimilation that they must rob 
other plants of all needed food or die of starvation. Some, 
like the cancer-root (seé Flora), are root-parasites ; others, 
like the dodder, are parasitic on stems above ground. The 
most dependent species of all, such as the flax-dodder, can 
live on only one kind of host, while the coarse orange- 
stemmed dodder,? which is common all over the central 
and the northeastern states, grows freely on many kinds 
of plants, from golden-rods to willows. 
407. Parasitic Cryptogams.— The wheat rust (Sect. 310) 
affords an excellent example of the relations between 
parasitic fungi and their hosts. The illustration showing 
the potato blight escaping from a stoma of the potato leaf 
(Fig. 191) shows plainly one way in which a microscopic 
parasite finds its way out of the tissues of the host-plant 
to ripen and scatter its spores. 
2 Alectorolophus hirsutus. 
2 Cuscuta Gronovii. 
