46 
fal ees 
to isolate them to study the conditions under which they live, their development and the 
extent of their ravages, and thus, by knowing their habits, to know at the same time their 
subsequent occurence, and to prevent their multiplication. 
It is, however, rare for these Cryptogams to occur isolated. There exist, moreover, 
a certain number of forms which inhabit our houses, and are found together on the same 
leaves, frequently with others growing upon them. 
When the parasitic fungi have penetrated the surface and attacked the substance of 
the leaf, the saprophytes which live upon the products of decomposition introduce them- 
selves, whereupon the destruction of the leaf progresses rapidly, and the microscope can 
neither furnish precise indication of the nature of the disease, nor of its origin, the fungi 
being so much mixed up with other vegetation. 
It sometimes happens, indeed, as in the case of the fungus which sometimes attacks 
the Vanilla in the Seychelle islands, Calospora Vanillae, that the same fungus undergoes 
successive transformations as the disease spreads over the leaf. Thus the species in question, 
C. Vanillae, had already received three different names before the common origin of its 
three forms was known. 
Supposing, indeed, that we are able to isolate and determine the different fungi present 
it is impossible, without knowing thoroughly the life history of each, either to say which 
form commenced the attack, and opened the way for the others, or what would be useful to 
check the spread of the disease. With four, five, or even ten different fungi present, how can 
we determine the parts played by each in the mischief? In such cases one must proceed to 
cultivate the species separately, and submit them to prolonged observation. One learns 
thus their nature and habits. Afterwards, if traces of analogous wounds are found on the 
leaves, their origin can immediately be determined. 
Thus we see how much research is necessary to obtain a definite result on such a 
subject. It is much to be desired that amateurs should facilitate these researches by sending 
materials, namely the diseased leaves which they find in their houses, to the laboratories 
established for this purpose, especially to the one which the Botanical Society of Brussels 
has recently established. 
It is very important to cut the leaves a soon as the disease appears, and not when it 
is too far advanced to enable one to determine the origin. 
Sometimes, indeed, when the damage is first observed, the fungus itself, which has 
caused it has already disappeared, having accomplished its work. This is the case, for 
example, with the potato disease. The fungus dies after having destroyed the substance of 
the leaf, and when these become black the mischief is already done, beyond all possible 
remedy. The only things which we can then discover with the microscope are the various 
saprophytes which have succeeded the original parasite, now only represented by spores. 
* 
We may now speak of the methods of combatting the fungi. 
These parasites generally develop when the houses are kept too hot or too cold, 
especially when the air is too close, and too much charged with stagnant humidity. In 
order to expel the fungi, we should therefore ventilate the houses as much as possible, 
and keep the temperature within proper limits, and observe generally all the precautions 
which tend to produce healthy growth. 
On the other hand, as we cannot entirely prevent the introduction of the fungi into our 
houses, we must examine the leaves from time to time, and wash them with weak tobacco 
(To be continued on p. 48.) 
cro? 
