DISEASES OF CULTIVATED PLANTS 329 
penetrate the bark of a tree for example, if aided by rifts caused by 
freezing or similar disturbances, to say nothing of the openings 
offered by wounds, the breaking of branches, etc. A recent illustra- 
tion of the danger of rifts in the bark of trees is offered by the 
chestnut disease which is proving so destructive near New York 
City. Few parasitic fungi have that penetrating power of thrusting 
the haustoria through the plant covering such as we find in the case 
of the dodder that twines about and robs the wild herbs and shrubs 
of the woods and fields as well as the cultivated flax and clovers. 
HOW PARASITIC FUNGI AFFECT THE HOST 
We know the cumulative effects of insufficient food supply; these 
effects must hold for plants attacked by parasitic fungi. Aside from 
the nutriment diverted to the parasite, there is reduced functional 
vigor of leaf, stem or root, and the loss becomes increased in this 
way. Letallthe leaves be parasitized, or let even three-fourths of 
them be entirely soattacked, and we may look for great loss of foliage, 
possibly entire loss of fruit and the detailed effects of diminished 
vigor, unripened wood, or by repetition, entire destruction of the 
host. Usually the effects are of many gradations, but in all cases of 
leaf-parasites the entire plant must suffer. We have learned that 
bacteria may, in a suitable medium, destroy themselves by the 
formation or emission of poisonous products. which are fatal alike to 
the bacteria and to animals, or even man; that such takes place within 
plants parasitized by fungi remains in doubt, and may be disre- 
garded for the present. The results of impaired function in the 
parts are serious enough to demand our attention. It is altogether 
‘probable that future investigations will modify our views upon 
some points. 
There are many curious transformations and malformations 
resulting from the attacks of parasitic fungi, simply by the multi- 
plication of cells of wound cork or other tissues in the effort of the 
host to shut off the fungus, not because the fungus consists of such 
amass of tissues. (See leaf-curl of peach). 
While exceedingly interesting to trace the effects of the white 
mold on shepherd’s purse and on the garden purslane, as well as the 
effects of bramble rust, cabbage club-root and a number of others, 
the principle above pointed out will be found generally applicable, 
and it is to the reactions of the host plant that the excrescences or 
malformations are chiefly attributable. 
It may further be stated that artificial cultures of parasitic fungi, 
either upon culture media or living plants are constantly adding to 
our knowledge in these lines. 
BENEFICIAL ORGANISMS: ROOT NODULES, ETC. 
While realizing the losses caused by parasitic fungi and bacteria 
we may not hastily condemn all fungi and bacteria. One of the most 
profound influences of aging culture of the soil is the beneficial 
