IOWA ACADEMY OF SCIENCE 
45 
ready for the entrance of fungi. Especially is this true of the spores of rust 
fungi which under warm and humid conditions germinate and then readily 
enter the host plant. 
Acclimatization. Many plants of arid regions are affected with fungi, though 
of course never so seriously as in more humid regions. The plant itself for 
want of acclimatization may become subject to disease, as will he shown later. 
The whole subject of health and disease is a complicated one and involves a 
great many factors. For a discussion of some of these problems the works of 
Marshall Ward^^ Gallo way^^ Bolley^^ Sachs^% PfeffeF®, JosF^, Kuster^®, Tu- 
beuP, Sorauer^®, De Bary^\ Wolf and ZopF^ should be consulted. 
FUNGI AS THE CAUSE OF DISEASE. 
Many years ago the German chemist Liebig^® attached much importance to 
chemistry in a study of the diseases of plants. He argued that in the case of 
potato rot the plant is diseased and therefore yields lo the attacks of the potato- 
rot fungus. 
. It was long thought by the followers of Liebig that the analyses of dead 
plants or the soil which contained them would reveal the cause of disease. 
Later the studies of Boussingault changed the attitude of agriculture towards 
these problems, and the experiments of Sachs revolutionized the whole subject 
of plant physiology. 
De Bary^^ took a view of the matter different from that of Liebig because it 
had been conclusively shown that apparently healthy plants may be inoculated 
by a fungus and produce the characteristic disease. 
By the introduction of pure cultures of fungi and bacteria, a new era of 
investigation has been introduced which no longer leaves any doubt about the 
causal relationship of disease and the organism. For a study of parasitic 
fungus diseases the same rules should apply as in a study of bacterial diseases 
in animals and plants. 
THE KINDS OF PARASITIC FUNGI. 
The parasitic fungi have been grouped with regard to relationship to host 
under the following heads by Tubeuf: 
1. Epiphytes: (a) with haustoria which only sink into the outer mem- 
branes of the host; (b) with haustoria penetrating into the cavity of the host- 
cells. 
2. Endophytes: (a) with a mycelium which grows in the walls of the host- 
cell, and is generally nourished without the aid of haustoria; (b) with a 
i^Disease in Plants. 
^^The Health of Plants in Greenhouses. Yearbook U. S. Dept. Agr. 1895:247. 
^^Encyl. of Agr. 2:47-53. 
I'^Dectures on the Physiology of Plants. 
^®Physiology of Plants. Pflanzen-Physiologie. 
i^Lectures in Plant Physiology, 
ispathologische Pflahzenatoniie. 
^^Diseases of Plants. Engl, translation W. G. Smith. 
2<’Handbuch der Pflanzenkrankheiten. 
2iUntersuchungen uber die Brandpilze und die durch sie verursachten Krankheiten 
der Pflanzen. 
22Krankheinten der landwirthschaftlichen Nutzpflanzen durch Schmarotzerpflanzen. 
23Lectures in Agricultural Chemistry. 
24De Bary. Comparative Morphology and Biology of Fungi, Mycetozoa and Bacteria. 
