312 OHIO EXPERIMENT STATION: BULLETIN 214 
seeds of clover or alfalfa and to be present in the commercial seeds. 
While these have been treated in the weed manual they require 
mention here. The seedling plant of dodder first forms a 
root and sends upward a whitish stem which twines about the 
clover or other stem, and sends sucking branches into the stem 
interior. ‘These “‘haustoria’ extract food material from the clover 
stem—that is they rob it of its own substance. Upon the formation 
of such organs the root of the dodder dies off and the future ex- 
istence of these twining, strawlike stems is at the expense of the 
host plant. 
A similar state of parasitic existence is found in the broomrape 
tribe whose very small seeds are scattered through the soil. Such 
a broomrape is well known on hemp, and the same hemp broomrape 
also attacks tobacco in Kentucky and possibly in our state. We 
have found another broomrape attacking tobacco in one district of 
Brown county, Ohio, and the illustration shows its appearance on 
the tobacco roots. 
When the leaves of a plant are attacked these show the direct 
effects; the symptoms of parasitic leaf diseases are usually localized 
injury resulting in spotting and often in browning of the leaf parts. 
Leaves may dry up somewhat slowly and drop to the earth, and yet 
the leaf tissues are simply dried up. Such conditions may result 
from late frost as upon shade, fruit, or ornamental trees. A most 
interesting case was once studied upon catalpa as a result of a frost 
in May. In that case the drying up was none the less to be expected 
at that time. 
An even more interesting case of leaf drying and dropping was 
upon young catalpa trees ina nursery caused by the attacks of a 
root-rot fungus, Zhzelavia. Owing to the death of many of the 
rootlets and finer roots as a result of the root-rot trouble, the leaves 
of these young trees dried up prematurely in August and Septem- 
ber and the leaves all dropped off. Thus we may have leaf 
dropping as a result of frost, injury by hail, noOE impairment 
or localized parasitic attack. 
LEAF SPOT AND SHOT-HOLE EFFECTS 
Leaf-spot symptoms are everywhere abundant and are really 
of very diverse origin. In any example in which the leaf tissues are 
locally invaded by a parasitic fungus we may expect evident effects. 
In the downy mildew troubles there may be wet-rot symptoms 
when the weather is moist, as in the case of Phytophthora or late 
blight attacking potato or tomato leaves; after the leaves have be- 
come badly diseased they may appear to die very suddenly because 
