E. J. BUTLER 3 



themselves to neighbouring objects such as other plants, insects which visit 

 plants, and even the person and implements of people passing through infected 

 fields or working in them.^ 



These properties of the spores render tliom peculiarly suited for dissemin- 

 ation. For short distance spread, currents of air are unquestionably the 

 most important means in the great majority of cases. The splashing of rain, 

 accompanied by the flapping of wet leaves against one another, is the chief 

 means in a few cases, as in the bean anthracnose, and is a secondary means in 

 others, as in potato blight. Adhesion by contact is well known to cause much 

 of the bunt in wheat, when wind-borne spores or broken bunt balls get into 

 the seed grain. Spread by insects takes place in certain well-established cases, 

 and is highly probable in others. The ergots of rye {Claviceps fuvpurea) and 

 other grasses are carried in part by Melanostoma mellina, Rhagonycha fulva, 

 etc., which are attracted by the sugary secretion that accompanies the Sphacelia 

 stage of the fungus, and carry the spores to other grass flowers. Pear blight, 

 [Bacillus (Micrococcus) amylov&rus] begins often in the stigma, to which the 

 bacillus is carried by insects (chiefly bees) from infected sap escaping from the 

 bark in spring. In Sclerotinia. urnula also the sweet-smelling spores are carried 

 by insects to the flowers of Vaccinia Vitis-idaea (cow-berry). In many cases 

 insects which cause wounds allow parasitic fungi to enter ; larch canker may 

 heglniTointheyvovindsoiColeopJiomlaricieUa and Chermes laricis ; Ceratostom- 

 ella filifera (a fungus which causes blueing of the wood of Pinus fonderosa) 

 from wounds of Dendroctonus ponderoscB and so on ; while the Nectrias which 

 cause canker of fruit and forest trees are said sometimes to be conveyed on 

 the bodies of the insects which cause wounds through which the fungi can 

 enter. Occasionally other animals have been accused of disseminating 

 disease ; mice are said to carry the spores of Fomes annosus, the cause of a 

 well-known pine disease, and snails those of a fir disease caused by Cucurhitaria 

 pityophila. Almost any disease may be carried by farm-workers, but the 

 cases of serious damage from this cause are rare. All soil-inhabiting fungi 

 are liable to be carried by irrigation water or surface wash after heavy rain ; 

 Fusarium wilts are undeniably carried from field to field by the latter ; and 

 there is evidence in India and elsewhere that diseased sugarcane stems thrown 

 into irrigation channels may enable the spores of the red rot fungus to reach 

 crops growing at a lower level. Infected soil may also carry the spores of 



1 In the Southern States it is said that experience has taught the peril of working in the 

 bean fields attacked by anthracnose on wet days, owing to the way the disease is carried on the 

 person and implements of the workers. We have evidence, too, that the Godavari palm disease 

 in India is often carried by those who climb the trees for the leaves, fruit and for teddy drawing 



