444 INSECTS AFFECTING VEGETATION 



adhere tc the seed grain as in the case of the smuts of grains gener- 

 ally, and second, and more exactly, those fungi which develop upon 

 or within the seed largely by their threads or mycelium, and may, 

 or may not, prevent the germination of the infested seed grain. Our 

 knowledge of these strictly seed infesting fungi is quite recent; we 

 may point to the work of Prof. Bolley and his assistants at the 

 North Dakota Experiment Station, especially upon the matter of 

 flax diseases; to the work of Dr. Halsted in New Jersey and to Bul- 

 letin 173 of the Ohio Station by Van Hook. With the tendency 

 to continuous growing of flax, in the west there was developed in 

 that new area specific seed and soil troubles which have been proved 

 to be perpetuated in the infected seed. An anthracnose of flax and 

 a Fusarium attacking flax seed are examples. 



No less conspicuous is the case of the blight fungus of peas, 

 Ascochyti pisi, which is also an anthracnose, and the allied anthrac- 

 nose of beans, Colletotrichum lagenarium. Investigations made at 

 the Ohio Station by Van Hook show the source of the trouble with 

 peas to be the infected seed employed and show also that seed treat- 

 ment will not destroy these internal fungi without destroying the 

 vitality of the seed. It was further shown that the source of relief 

 lies in growing healthy seed through the use of fungicides upon the 

 pea vines from which seed is gathered; likewise that infection may 

 remain in the soil. More recent work at the Ohio Station has shown 

 the presence of seed infesting and seed infecting diseases in wheat. 

 (See Bulletin 203.) It was also found in continuous wheat land as 

 much as 6 per cent of the young wheat plants were destroyed in the 

 fall by this same parasite which appears to survive in the soil under 

 continuous wheat growing as well as to be propagated in the seed 

 grain. 



PARASITIC FOLIAGE DISEASES. 



Foliage diseases of every sort are caused by oxygen loving or 

 aerobic species of parasites, and very often this development on the 

 leaves consists of the imperfect forms of the fungus life history. 

 These forms are none the less aggressive and injurious for this rea- 

 son, but the exact manner of survival from year to year becomes 

 important wherever not known. The application of this to prevent- 

 ive measures in the control of these diseases upon foliage and fruit is 

 seen in the case of apple scab, the monilia rot of plums, peaches, 

 cherries, etc., and in apple bitter-rot. These last two rot troubles 

 survive in the mummy or dry rotted fruits and this explains the rea- 

 son for the oft repeated injunction to destroy all mummies in addi- 

 tion to spraying operations. The bitter-rot of apples is propagated 

 by means of summer branch cankers on the tree, as brought out in 

 recent years. Other leaf forms survive on the fallen leaves or pos- 

 sibly in bud scales as with the leaf curl and bladders of the Exoascae. 

 A large number must live over on the branches. 



Parasites upon foliage soon become apparent from the spots on 

 the leaves and dropping of fruit resulting. This dropping may come 

 as a result of impaired vigor by reason of disease then it is later, 

 but is more often the direct result of parasitic attack by the disease 



