10 BULLETIN OF THE BUSSEY INSTITUTION. 
well understood, and may be produced in large quantities. Wood* 
has shown that the oxidases and peroxidases are capable of 
decomposing chlorophyll when especially active, resulting in the 
variegations of the green parts of plants. The mosaic disease of 
tobacco he was able to produce at will by increasing the action of 
these enzyms. Beijerinckt also induced albino diseases by inocu- 
lating healthy plants with the filtered juice of spotted ones, and 
concludes that the mosaic disease is due to an enzym contained in 
a **contagium fluidum vivum.”’ 
It has often been suggested that ‘* yellows” is a disease 
allied to variegation often found in other plants, and undoubtedly 
it is. According to Darwin,{ variegation seems to result from 
a feeble and atrophied condition of the plant, and a large pro- | 
portion of the seedlings raised from parents, both of which are 
variegated, usually perish at an early age. ‘The first indication 
that anything was wrong with the Hersey Rareripe was that the 
seeds failed to germinate. It is also well known that variegated 
plants if grafted on green ones may induce the development of 
variegated leaves on both stem and stock, and that variegation 
may be inherited through the seed. Darwin cites many instances 
of the peculiar constitutional variations of the peach. Oxydized 
enzyms being present in normal peach trees, any slight change 
in the environment might incite them to greater activity and a 
consequent destruction of chlorophyll. 
The objection which has always been brought against the enzym 
theory has been that the method by which the irritated enzym 
is carried from tree to tree is unknown. ‘That stocks budded 
from diseased trees, and tools used in pruning might transfer the 
enzyms is easily conceivable, but any proof as to the contamina- 
tion of seedling trees has been lacking until the history of the 
Hersey Rareripe Peach was known and the evidence carefully 
weighed. ‘The evidence shows that the enzyms were carried from 
tree to tree in the pollen. That the disease is communicated in 
this way was suggested as long ago as 1828 by William Prince, § 
who says of the ‘‘ yellows”: ‘* This disease is spread at the time 
* Centbi. Bak- 1899, V,p-. 745. 
+ Botanisches Centralblatt, 78. (1899) No. 5, pp. 146-151, abstracted 
from Separate Verhandlang K. Akad. Wetensch, Amsterdam, 1898. 
{ Animals and Plants under Domestication, Vol. II, p. 205. 
§ A Short Treatise on Horticulture. 
