BULLETIN OF THE BUSSEY INSTITUTION. i, 
soil and situation it is removed to another situation, rendering it 
in the meantime extremely susceptible to infirmities of all kinds. 
It is easy to suggest other reasons why the Magdalene has 
obtained so firm a hold. For instance, with our variable climate, 
the first season after its importation, and possibly the second, 
may have been milder or more even, and thus allowed more time 
for adjustment before unfavorable seasons were forced upon 
it. Again, the soil on which it was grown was not rich, and, 
unless heavily fertilized, less growth would be made each year 
than in a more fertile soil, thus increasing the probability of a 
better ‘‘ ripening” of the wood to withstand the cold blasts of 
winter, — a factor now recognized among our peach growers, who 
try to force most of the growth of the twigs early in the season. 
The experience of Mr. Hersey, together with the facts pre- 
viously stated, show that climate is more or less a factor in the 
question as to the cause of peach ‘‘ yellows”; yet experiments 
have shown that in some instances the disease may be communi- 
cated from one tree to another by budding, and by using tools in 
pruning a healthy tree after having come into contact with diseased 
tissues. Hence there must be some other factor not yet dis- 
cussed; and we now turn to the last item in the list of sugges- 
tions on page 1, entitled (f): for, since the ‘‘ yellows” behaves 
like an infectious disease and as experimental evidence has shown 
that it is not due to living organisms, the only alternative is that 
of enzyms.* 
The probability that enzyms may be the true cause is further 
enhanced by the discovery of Buchneryt that alcoholic fermenta- 
tion set up by the yeast plant is due to an enzym which he has 
separated from it. Enzyms are normally present in plants and 
animals, but being extremely sensitive to environment they may 
become abnormally active under certain conditions not as yet 
* Enzyms are secretions of protoplasm which provoke alterations (known 
as fermentations) in the cell contents, but do not usually enter into the 
changes themselves. They are classified according to the nature of the 
changes invoked, those causing oxidation are known as oxidases and peroxi- 
dases. For a further discussion of the nature and work of enzyms, see J. R. 
Green, ‘‘ The Soluble Ferments and Fermentations,” University Press, Cam- 
bridge, London, 1899; J. Effront, ‘‘ Les Enzymes et leurs Applications,” 
Carré et Naud, Paris, 1899. 
7 Berl. Ber. 1897, 3O. pp. 117, 1110. 
