BULLETIN OF THE BUSSEY INSTITUTION. 11 
when the trees are in bloom, and is disseminated by the pollen or 
farina blowing from the flowers of the diseased trees and impreg- 
nating the flowers of those which are healthy, and which is quickly 
circulated by the sap through the branches and fruit, causing the 
fruit, wherever the infection extends, to ripen prematurely.” Pro- 
fessor Smith evidently failed to appreciate the importance of this 
observation, and he has remarked that Prince ‘‘ does not always 
distinguish clearly between things proved and things probable.” 
Downing,* in his time, has said: ‘* Experiments have been made 
by dusting the pollen of diseased trees upon the blossoms of 
healthy ones without communicating the ‘ yellows.’”’ 
The inferences which were drawn from the experiments referred 
to by Downing are as onesided as are those of Mr. Prince. They 
show that Prince was wrong in inferring that the material in the 
pollen was quickly circulated by the sap and affected parts of the 
plant other than the impregnated ovule. Not until the attempt 
had been made to grow trees from such ovules was it safe to 
conclude that the disease was not carried by the pollen. With 
the Hersey Peach this experiment was carried out, and it shows 
that, although the disease was carried by the pollen, it was not 
communicated to the parent plant but affected the ovule only. 
Further evidence that pollen is the carrier of the disease, lies in 
the fact that only those trees whose ovules were susceptible of 
being fertilized with pollen of other varieties were attacked by the 
disease, while the White Magdalene which is sterile to foreign 
pollen has not been infected. 
It may be suggested by some that not enough infecting material 
could be carried by such small bodies as pollen grains, but only a 
very small amount of infecting material is necessary; and Smitht 
also says: ** Only a small amount of infective material is neces- 
sary, provided it be in the form of living cells, which can be 
induced to unite with the actively growing tissues of the tree.” 
And on the same page he says: ‘* Since diseased trees have been 
shown to be very full of infectious matter, it must be that for 
unknown reasons much of this fails to find an immediate entrance 
into healthy trees. Otherwise the peach would soon disappear 
entirely.” This ‘‘unknown” reason appears to be that the disease 
is communicated in nature only by means of pollen, yet he seems 
* Fruit and Fruit Trees of America, p. 463. 
¢t Bull. 1, Div. Veg. Path. U. S. Dept. Agr., p. 44. 
