672 Hygiene of House Plants. [ November, 
growth, but after this has continued until the plant has sufficient 
vigor, it produces flowers and fruit, unless it belong to one of 
the lower orders. Now the usual conditions may be somewhat 
changed ; the temperature of the plant rises ten or more degrees 
above that of the surrounding air, and as flowers expand, car- 
bonic acid passes off and oxygen is taken up, but in most cases 
this is not of such extent as to be important. 
A greater effect is that of the odors which some flowers possess. 
We have very little positive knowledge of the nature of the per- 
fumes of flowers. We know that powerful odors affect some per- 
sons unfavorably, at least at the time they are inhaled, causing 
nausea and faintness. We know that hydrocyanic acid and other 
deleterious substances exist in some odors, but I believe that all 
odors from plants which are known to contain injurious substances 
are disagreeable and repulsive. It seems possible at least that 
intense odors, such as that of the tuberose or many lilies, if in- 
haled for a long time would prove harmful, while the more mild 
odors are not so. There is very good authority for the assertion 
that many plants, such as the lemon, mint, hyacinth, heliotrope, 
mignonette, etc., when in bloom, in some way increase the quan- 
tity of ozone in the surrounding air, and are in this way benefi- 
cial. The common sunflower is said to be very useful in this 
way, and to do very much to counteract the effect of miasmatic 
vapors in its neighborhood. ‘Those resinous odors which come 
from coniferous trees are agreeable to every one, and are gen 
erally believed to be wholesome and remedial. The blue-gum 
(Eucalyptus) of Australia emits camphorated and antiseptic 
vapors which have been found of great value in malarial regions. 
On the whole ‘it seems probable that the perfumes of most of 
our house plants are not very powerful for either good or evil, 
but that they are quite as likely to be beneficial as the reverse 
If decaying leaves or other such débris are allowed to remain on 
the surface of the pots, they may vitiate the air; but aside from 
this it is not probable that injurious gases can come from decom- 
posing material in the earth of the pots, for the plant and the 
earth together act vigorously to prevent any such thing. 
We conclude, then, that house plants are injurious only as they 
increase the carbonic acid in the air, and as they give out jati 
ous perfumes. We have found that the first of these effects 15 
certainly far more than counterbalanced by the taking up of pad 
bonic acid and the throwing out of oxygen, and the second 1s yee 
probably fully neutralized. House plants are positively — 
SE pe ee Ree Pe oF IE ee EEES 
